plpgsql: add support for set-returning functions

This commit adds support for set-returning PL/pgSQL functions. Unlike SQL
SRFs, PL/pgSQL SRFs add to the result set at arbitrary points during
execution using `RETURN NEXT` (scalar) and `RETURN QUERY` (relational)
statements. We support this feature by allocating a `RoutineResultBufferID`
that allows the sub-routines that implement the PL/pgSQL routine body to
access the SRF's result buffer directly during execution.

Fixes #105240

Release note (sql change): Set-returning PL/pgSQL functions are now
supported. A PL/pgSQL SRF can be created by declaring the return type
as `SETOF <type>` or `TABLE`.

Author: DrewKimball

pkg/ccl/logictestccl/testdata/logic_test/plpgsql_srf

@@ -10,12 +10,6 @@ CREATE OR REPLACE PROCEDURE foo() AS $$
   END
 $$ LANGUAGE PLpgSQL;
 
-statement error pq: unimplemented: set-returning PL/pgSQL functions
-CREATE OR REPLACE FUNCTION bar() RETURNS SETOF INT LANGUAGE PLpgSQL AS $$ BEGIN RETURN NEXT 100; END $$;
-
-statement error pq: unimplemented: set-returning PL/pgSQL functions
-CREATE OR REPLACE FUNCTION bar() RETURNS TABLE (x INT) LANGUAGE PLpgSQL AS $$ BEGIN RETURN NEXT 100; END $$;
-
 subtest error_detail
 
 # Regression test for #123672 - annotate "unsupported" errors with the

pkg/ccl/logictestccl/testdata/logic_test/plpgsql_unsupported

@@ -12,7 +12,7 @@ go_test(
         "//build/toolchains:is_heavy": {"test.Pool": "heavy"},
         "//conditions:default": {"test.Pool": "large"},
     }),
-    shard_count = 32,
+    shard_count = 33,
     tags = ["cpu:2"],
     deps = [
         "//pkg/base",

pkg/ccl/logictestccl/tests/3node-tenant/generated_test.go

@@ -12,7 +12,7 @@ go_test(
         "//build/toolchains:is_heavy": {"test.Pool": "heavy"},
         "//conditions:default": {"test.Pool": "large"},
     }),
-    shard_count = 32,
+    shard_count = 33,
     tags = ["cpu:2"],
     deps = [
         "//pkg/base",

pkg/ccl/logictestccl/tests/fakedist-disk/BUILD.bazel

@@ -12,7 +12,7 @@ go_test(
         "//build/toolchains:is_heavy": {"test.Pool": "heavy"},
         "//conditions:default": {"test.Pool": "large"},
     }),
-    shard_count = 33,
+    shard_count = 34,
     tags = ["cpu:2"],
     deps = [
         "//pkg/base",

pkg/ccl/logictestccl/tests/fakedist-disk/generated_test.go

@@ -9,7 +9,7 @@ go_test(
         "//pkg/ccl/logictestccl:testdata",  # keep
     ],
     exec_properties = {"test.Pool": "large"},
-    shard_count = 31,
+    shard_count = 32,
     tags = ["cpu:1"],
     deps = [
         "//pkg/base",