builtins: array_to_string should traverse nested arrays

[msirek]

Fixes #95588

In Postgres, array_to_string traverses nested arrays and prints their contents. In CRDB, the nested array structures are printed out. For example,
SELECT array_to_string(ARRAY[ARRAY[ARRAY[5,6], ARRAY[2,3]]], ' ');

CRDB Result: ARRAY[ARRAY[5:::INT8,6:::INT8],ARRAY[2:::INT8,3:::INT8]] Postgres Result: 5 6 2 3

This fix brings the behavior of array_to_string in line with Postgres, and avoids printing the nested ARRAY structures.

Some tools like GoldenGate rely on Postgres-compatible behavior of array_to_string for proper functioning.

Release note (bug fix): This patch fixes the array_to_string built-in function so that nested arrays are traversed without printing 'ARRAY' at each nesting level.

[cockroach-teamcity]

This change is 

[yuzefovich]

Nice! Let's add backport labels to this since it seems like a pretty safe fix.

Reviewed 2 of 2 files at r1, all commit messages.
Reviewable status: complete! 1 of 0 LGTMs obtained (waiting on @msirek)

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pkg/sql/sem/builtins/builtins.go line 9876 at r1 (raw file):

		} else {
			if nestedArray, ok := arr.Array[i].(*tree.DArray); ok {
				arrayToStringHelper(evalCtx, nestedArray, delim, nullStr, f)

nit: consider adding a quick comment that we want to "unpack" nested arrays to be consistent with postgres.

[msirek]

Added

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

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pkg/sql/sem/builtins/builtins.go line 9876 at r1 (raw file):

Previously, yuzefovich (Yahor Yuzefovich) wrote…

nit: consider adding a quick comment that we want to "unpack" nested arrays to be consistent with postgres.

Done

[msirek]

TFTR!
bors r=yuzefovich

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

[craig]

Build succeeded:

• Bazel Essential CI (Cockroach)

[blathers-crl]

Encountered an error creating backports. Some common things that can go wrong:

1. The backport branch might have already existed.
2. There was a merge conflict.
3. The backport branch contained merge commits.

You might need to create your backport manually using the backport tool.

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error creating merge commit from eb88269 to blathers/backport-release-22.1-95802: POST https://api.github.com/repos/cockroachdb/cockroach/merges: 409 Merge conflict []

you may need to manually resolve merge conflicts with the backport tool.

Backport to branch 22.1.x failed. See errors above.

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