Finish support for list-of-targets

[mbs-octoml]

This finishes the work started in #11173 to support
'external codegen' targets in the N build-like API surfaces, which in turn requires all the
Relay-level build interfaces to support list-of-targets instead of dictionary-of-targets. And
prepare for plumbing targets through the external codegen machinery.

(See https://discuss.tvm.apache.org/t/byoc-supporting-cutlass-byoc-with-collage/12796/6 for
more context on build/target changes, and https://github.com/apache/tvm-rfcs/blob/main/rfcs/0062-collage.md
for the overall Collage RFC).

• It turns out it's ok if a build is given only a single 'external codegen' target, so remove that check
  in CompilationConfig::Init. (When Collage builds a 'candidate partition' it does so for a single target.
  As far as Collage is concerned it does not care whether the target is regular (eg Target("cuda")), or
  for a specific external codegen (eg Target("cutlass")), it just passes the target into the build.)

• Add CompilationConfig::FindPrimitiveTargetForKind which I'll later need to retrieve
  the external codegen Target instance corresponding to a "Compiler" attribute value.

• Target.update_target_host_consist was supporting three API styles:

  • single target
  • map from device type to target
  • map from target to IRModule (for the ir_to_runtime API)

  I replaced all those calls with a more specialized 'canonicalize' call:

  • Target.canonicalize_target_and_host
  • Target.canonicalize_multi_targets_and_host
  • Target.canonicalize_target_map_and_host

  In particular, all the tuning interfaces (task extraction, tuning, tuning records) all explicitly
  do not support multiple targets since that just doesn't make sense.

• Rev the micro library format version from 5 to 6 since the 'target' attribute in the metadata.json
  output is now an array rather than a dictionary. Remove the N uses of target.values() to follow
  suite.

[SebastianBoblest]

Have you thought about structuring tests into classes according to the function under test?
Like
class TestCanonMultiTargetAndHost:
def test_with_tvm_objects(self):
# this test here

The names of tests can then be shorter and more descriptive at the same time.
This is more a question than a suggestion.

[mbs-octoml]

Not really experienced with good pytest style, just mimicking whatever I happen to find already in place. Happy to try that if it's considered the preferred idiom?

[jwfromm]

This overall LGTM. Thank you @mbs-octoml!

[vinx13]

Hi @mbs-octoml with this PR I'm seeing some warnings UserWarning: target_host parameter is going to be deprecated. Please pass in tvm.target.Target(target, host=target_host) instead. even if I don't use target_host. Would you mind taking a look? It can be reproduced with the following script

import tvm
from tvm import te
target = tvm.target.Target('nvidia/geforce-rtx-3070')
N = 32
A = te.placeholder(name='A', shape=[N])
B = te.compute((N,), lambda i,: A[i] + 1.0)
sch = te.create_schedule(B.op)
sch[B].bind(sch[B].op.axis[0], te.thread_axis('threadIdx.x'))
tvm.build(sch, [A, B], target)

[mbs-octoml]

#11499