sql: add and link Postgres type i/o builtins

[jordanlewis]

In Postgres, every type has 4 i/o builtins that correspond to it. For int8, for instance, there's int8in, int8out, int8send, and int8recv. We implement these as no-op builtins for ORM compatibility.

Additionally, we link these builtins to their corresponding fields in pg_type for all types.

Also, fix the name in pg_type for our Tuple type, which is called record in Postgres.

Fixes #12526.

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This change is 

[knz]

Woo, so many thanks for tackling this.
Two nits remaining though.

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Reviewed 2 of 5 files at r1, 3 of 3 files at r2.
Review status: all files reviewed at latest revision, 2 unresolved discussions, all commit checks successful.

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pkg/sql/parser/pg_builtins.go, line 36 at r2 (raw file):

// programmatically determine whether or not this underscore is present, hence
// the existence of this map.
var typeBuiltinsHaveUnderscore = map[oid.Oid]bool{

map[oid.Oid]struct{}{ ... }

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pkg/sql/parser/pg_builtins.go, line 91 at r2 (raw file):

	return map[string][]Builtin{
		builtinPrefix + "send": {
			Builtin{

I'd make a function returning a Builtin that takes just the desired return type and argument type as arguments, to construct the four things.

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Comments from Reviewable

[jordanlewis]

TFTR!

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Review status: 1 of 5 files reviewed at latest revision, 2 unresolved discussions.

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pkg/sql/parser/pg_builtins.go, line 36 at r2 (raw file):

Previously, knz (kena) wrote…

map[oid.Oid]struct{}{ ... }

Done.

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pkg/sql/parser/pg_builtins.go, line 91 at r2 (raw file):

Previously, knz (kena) wrote…

I'd make a function returning a Builtin that takes just the desired return type and argument type as arguments, to construct the four things.

good call. done

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Comments from Reviewable

[knz]

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Reviewed 2 of 4 files at r3, 3 of 3 files at r4.
Review status: all files reviewed at latest revision, all discussions resolved, all commit checks successful.

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Comments from Reviewable

[nvanbenschoten]

Late to the game, but this is great! Really nice job.

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Review status: all files reviewed at latest revision, 1 unresolved discussion, all commit checks successful.

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pkg/sql/pg_catalog.go, line 1462 at r3 (raw file):

				h.RegProc(builtinPrefix+"in"),   // typinput
				h.RegProc(builtinPrefix+"out"),  // typoutput
				h.RegProc(builtinPrefix+"recv"), // typrecv

nit: Why did this comment get changes? The column is typreceive.

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Comments from Reviewable