colexecspan: de-templatize span assembler and use span.Splitter

[RaduBerinde]

colexecspan: de-templatize span assembler

The span assembler code is generated only to inline a piece of code
that has two variants. This change converts it to non-generated code
and simply forks the code paths above the batch loop.

Release note: None

colexecspan: use span.Splitter

The span assembler duplicates some of the logic in span.Splitter.
Now that the latter is a separate type, we can use it instead.

Release note: None

[cockroach-teamcity]

This change is 

[yuzefovich]

Reviewed 1 of 1 files at r1, 6 of 6 files at r2, 3 of 3 files at r3, all commit messages.
Reviewable status: complete! 1 of 0 LGTMs obtained (waiting on @RaduBerinde)

---

-- commits, line 2 at r1:
In order to not break the build (and keep the bisect working), we need to do the same changes in span_assembler_gen.go and colexecspan/BUILD.bazel.

---

pkg/sql/span/span_splitter.go, line 87 at r3 (raw file):

}

// FamilyIDs returns the family IDs into which spans will be split, or nil if

nit: maybe add this as a comment on neededFamilies too.

[RaduBerinde]

TFTR!

Reviewable status: complete! 1 of 0 LGTMs obtained (waiting on @yuzefovich)

---

-- commits, line 2 at r1:

Previously, yuzefovich (Yahor Yuzefovich) wrote…

In order to not break the build (and keep the bisect working), we need to do the same changes in span_assembler_gen.go and colexecspan/BUILD.bazel.

I just squashed the commits, it was only to make the review easier.

[RaduBerinde]

bors r+

[craig]

Build failed (retrying...):

• GitHub CI (Cockroach)

[craig]

Build succeeded:

• GitHub CI (Cockroach)