release-23.2: sql: allow dropping routines with UDT-typed parameters

[blathers-crl]

Backport 1/1 commits from #115848 on behalf of @DrewKimball.

/cc @cockroachdb/release

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Previously, it was not possible to specify UDT parameters when dropping a routine. This is because of an oversight in MatchAtIdentical, which was likely copied from MatchAt. Specifically, MatchAt has special handling for tuple types that take advantage of the fact that types.Equivalent allows types.AnyTuple to match with any other tuple. MatchAtIdentical, on the other hand, uses types.Identical, which does not make the same allowance. This meant that overload resolution would always fail for UDT parameters in code paths that use MatchAtIdentical`, such as DROP FUNCTION.

This patch removes the replacement logic for tuple types in MatchAtIdentical, so that types.Identical is always called with the original type. This allows statements like the following to succeed:

DROP PROCEDURE foo(x udt);

Fixes #114677

Release note (bug fix): Fixed a bug existing since v23.1 that prevented naming UDT parameters when dropping a user-defined function (or procedure).

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Release justification: Fixes a bug that prevents DROP FUNCTION with a UDT parameter.

[blathers-crl]

Thanks for opening a backport.

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[cockroach-teamcity]

This change is 

[rharding6373]

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