pgsql: Track nesting depth correctly when drilling down into RECORD Var

Track nesting depth correctly when drilling down into RECORD Vars.

expandRecordVariable() failed to adjust the parse nesting structure
correctly when recursing to inspect an outer-level Var.  This could
result in assertion failures or core dumps in corner cases.

Likewise, get_name_for_var_field() failed to adjust the deparse
namespace stack correctly when recursing to inspect an outer-level
Var.  In this case the likely result was a "bogus varno" error
while deparsing a view.

Per bug #18077 from Jingzhou Fu.  Back-patch to all supported
branches.

Richard Guo, with some adjustments by me

Discussion: https://postgr.es/m/18077-b9db97c6e0ab45d8@postgresql.org

Branch
------
REL_14_STABLE

Details
-------
https://git.postgresql.org/pg/commitdiff/ae13f8166dc372a94e596f423790a67abd7bf68c

Modified Files
--------------
src/backend/parser/parse_target.c      | 20 ++++++++----
src/backend/utils/adt/ruleutils.c      | 37 ++++++++++++---------
src/test/regress/expected/rowtypes.out | 60 ++++++++++++++++++++++++++++++++++
src/test/regress/sql/rowtypes.sql      | 25 ++++++++++++++
4 files changed, 120 insertions(+), 22 deletions(-)