[observability] fix EXPLAIN ANALYZE to work on objects that are not in a database (#34216)

@ggevay noticed that `EXPLAIN ANALYZE CPU FOR INDEX
mz_internal.mz_console_cluster_utilization_overview_ind;` was returning
empty results. It turns out that `mz_internal.mz_mappable_objects`
assumed that every object it worked with lived in a database, but this
is not the case for objects in `mz_internal`. Changing the join on
`mz_databases` to be a `LEFT JOIN` should resolve the issue.

I did not bother doing something similar for the schema, as I believe
every object must live in a schema. I extended the `EXPLAIN ANALYZE`
testdrive to account for this bug.

### Motivation

  * This PR fixes a recognized bug.

Original message:
https://materializeinc.slack.com/archives/C08ACQNGSQK/p1763565268661699
Follow-up thread:
https://materializeinc.slack.com/archives/C08ACQNGSQK/p1763565268661699

### Checklist

- [ ] This PR has adequate test coverage / QA involvement has been duly
considered. ([trigger-ci for additional test/nightly
runs](https://trigger-ci.dev.materialize.com/))
- [ ] This PR has an associated up-to-date [design
doc](https://github.com/MaterializeInc/materialize/blob/main/doc/developer/design/README.md),
is a design doc
([template](https://github.com/MaterializeInc/materialize/blob/main/doc/developer/design/00000000_template.md)),
or is sufficiently small to not require a design.
  <!-- Reference the design in the description. -->
- [ ] If this PR evolves [an existing `$T ⇔ Proto$T`
mapping](https://github.com/MaterializeInc/materialize/blob/main/doc/developer/command-and-response-binary-encoding.md)
(possibly in a backwards-incompatible way), then it is tagged with a
`T-proto` label.
- [ ] If this PR will require changes to cloud orchestration or tests,
there is a companion cloud PR to account for those changes that is
tagged with the release-blocker label
([example](MaterializeInc/cloud#5021)).
<!-- Ask in #team-cloud on Slack if you need help preparing the cloud
PR. -->
- [ ] If this PR includes major [user-facing behavior
changes](https://github.com/MaterializeInc/materialize/blob/main/doc/developer/guide-changes.md#what-changes-require-a-release-note),
I have pinged the relevant PM to schedule a changelog post.

Author: mgree

src/catalog/src/builtin.rs

@@ -6174,12 +6174,12 @@ pub static MZ_MAPPABLE_OBJECTS: LazyLock<BuiltinView> = LazyLock::new(|| {
         ("global_id", "The global ID of the object."),
     ]),
     sql: "
-SELECT quote_ident(md.name) || '.' || quote_ident(ms.name) || '.' || quote_ident(mo.name) AS name, mgi.global_id AS global_id
+SELECT COALESCE(quote_ident(md.name) || '.', '') || quote_ident(ms.name) || '.' || quote_ident(mo.name) AS name, mgi.global_id AS global_id
 FROM      mz_catalog.mz_objects mo
-     JOIN mz_introspection.mz_compute_exports mce ON (mo.id = mce.export_id)
-     JOIN mz_catalog.mz_schemas ms ON (mo.schema_id = ms.id)
-     JOIN mz_catalog.mz_databases md ON (ms.database_id = md.id)
-     JOIN mz_introspection.mz_dataflow_global_ids mgi ON (mce.dataflow_id = mgi.id);",
+          JOIN mz_introspection.mz_compute_exports mce ON (mo.id = mce.export_id)
+          JOIN mz_catalog.mz_schemas ms ON (mo.schema_id = ms.id)
+          JOIN mz_introspection.mz_dataflow_global_ids mgi ON (mce.dataflow_id = mgi.id)
+     LEFT JOIN mz_catalog.mz_databases md ON (ms.database_id = md.id);",
     access: vec![PUBLIC_SELECT],
 }
 });

test/testdrive/explain-analyze.td

@@ -7,7 +7,7 @@
 # the Business Source License, use of this software will be governed
 # by the Apache License, Version 2.0.
 
-$ set-regex match=((\d+)\sbytes|u(\d+)|(\d+:\d+:\d+.\d+)) replacement=<XXX>
+$ set-regex match=((\d+)\sbytes|u(\d+)|s(\d+)|(\d+:\d+:\d+(.\d+)?)) replacement=<XXX>
 
 # In case the environment has other replicas
 > SET cluster_replica = r1
@@ -58,3 +58,77 @@ operator                      total_memory   total_records
 object                      global_id    total_elapsed
 ------------------------------------------------------
 materialize.blue.t_idx      <XXX>        <XXX>
+
+# ensure we can explain mz_internal objects
+
+> SET CLUSTER = mz_catalog_server;
+
+> EXPLAIN ANALYZE CPU FOR INDEX mz_internal.mz_console_cluster_utilization_overview_ind;
+operator                     total_elapsed
+-----------------------------------------
+"Arrange (#17{cluster_id})" <XXX>
+"  Stream <XXX>" <null>
+"Returning Map/Filter/Project" <XXX>
+"  Union" <XXX>
+"    Read l4" <XXX>
+"    Map/Filter/Project" <XXX>
+"      Consolidating Union" <XXX>
+"        Read l3" <XXX>
+"        Negate Diffs" <XXX>
+"          Read l4" <XXX>
+"With l4 = Differential Join %1 » %0" <XXX>
+"  Arrange (#1, #0)" <XXX>
+"    Non-incremental GroupAggregate`" <XXX>
+"      Arranged <XXX>" <XXX>
+"  Arrange (#0{replica_id}, #3{bucket_start})" <XXX>
+"    Stream l3" <null>
+"l3 = Differential Join %1 » %0" <XXX>
+"  Arrange (#0, #1)" <XXX>
+"    Map/Filter/Project" <XXX>
+"      Non-monotonic TopK" <XXX>
+"        Differential Join %1 » %0" <XXX>
+"          Arranged <XXX>" <null>
+"          Arrange (#0{replica_id})" <XXX>
+"            Distinct GroupAggregate" <XXX>
+"              Read l2" <XXX>
+"  Arrange (#0, #3)" <XXX>
+"    Stream l2" <null>
+"l2 = Delta Join [%0 » %1 » %2 » %3 » %4 » %5][%1 » %0 » %2 » %3 » %4 » %5][%2 » %0 » %1 » %3 » %4 » %5][%3 » %0 » %1 » %2 » %4 » %5][%4 » %0 » %1 » %2 » %3 » %5][%5 » %0 » %1 » %2 » %3 » %4]" <XXX>
+"  Arrange (#0{replica_id})" <XXX>
+"    Arranged l0" <null>
+"  Arrange (#0{replica_id}, #3{bucket_start})" <XXX>
+"    Map/Filter/Project" <XXX>
+"      Non-monotonic TopK" <XXX>
+"        Read l1" <XXX>
+"  Arrange (#0{replica_id}, #4{bucket_start})" <XXX>
+"    Map/Filter/Project" <XXX>
+"      Non-monotonic TopK" <XXX>
+"        Read l1" <XXX>
+"  Arrange (#0{replica_id}, #3{bucket_start})" <XXX>
+"    Map/Filter/Project" <XXX>
+"      Non-monotonic TopK" <XXX>
+"        Read l1" <XXX>
+"  Arrange (#0{replica_id}, #3{bucket_start})" <XXX>
+"    Map/Filter/Project" <XXX>
+"      Non-monotonic TopK" <XXX>
+"        Read l1" <XXX>
+"  Arrange (#0{replica_id}) (#0{replica_id}, #3{bucket_start})" <XXX>
+"    Map/Filter/Project" <XXX>
+"      Non-monotonic TopK" <XXX>
+"        Read l1" <XXX>
+"l1 = Differential Join %0 » %1" <XXX>
+"  Arrange (#1{replica_id})" <XXX>
+"    Map/Filter/Project" <XXX>
+"      Accumulable GroupAggregate" <XXX>
+"        Map/Filter/Project" <XXX>
+"          Delta Join [%0 » %2 » %1][%1 » %0 » %2][%2 » %0 » %1]" <XXX>
+"            Arranged <XXX>" <null>
+"            Arranged <XXX>" <null>
+"            Arrange (#0{replica_id}) (#1{size})" <XXX>
+"              Arranged l0" <XXX>
+"  Arrange (#0{replica_id})" <XXX>
+"    Arranged l0" <XXX>
+"l0 = Distinct GroupAggregate" <XXX>
+"  Union" <XXX>
+"    Arranged <XXX>" <XXX>
+"    Arranged <XXX>" <XXX>