26621:  sql,opt: propagate composite types (labeled tuples) r=knz a=knz

Needed to resolve #24866.

This patch adds more complete support for composite types (labeled
tuples) by ensuring the following:

- tuple labels are preserved during constant folding of tuple
  expressions.
- tuple labels are preserved during expression transformations
  in optimizations.
- subqueries in scalar contexts receive a composite type with labels.

Note that there is currently a bug in DTuple serialization which break
composite literals in distributed execution, so the composite type
support is not fully ready yet.
This is tracked as separate bug #26624.

Release note: None

26683: opt: don't push limit through project when ordering on synthesized column r=RaduBerinde a=RaduBerinde

It is invalid to push limit/offset through a projection if the
ordering depends on a synthesized column. Fix the rules to check for
this.

Release note: None

Co-authored-by: Raphael 'kena' Poss <knz@cockroachlabs.com>
Co-authored-by: Radu Berinde <radu@cockroachlabs.com>

26628: sql: Support tuple column access and tuple stars r=knz a=knz

First commits from #26621.
Completes the fix to #24866 by re-activating disabled tests.
This work is yet another step towards #16971. It would actually fix #16971 if it were not for #26627, #26624 and #26629.

This work is yet another step towards #16971.

The labeled tuples introduced in #25283 can now be accessed using
their labels or using a star, e.g. `(E).*`.

Release note (sql change): Labeled tuples can now be accessed using
their labels (e.g. `SELECT (x).word FROM (SELECT pg_expand_keywords()
AS x)` or a star (e.g. `SELECT (x).* FROM (SELECT pg_expand_keywords()
AS x)`).

Fixes #26720.

Co-authored-by: Raphael 'kena' Poss <knz@cockroachlabs.com>
Co-authored-by: Bram Gruneir <bram@cockroachlabs.com>