28944: sql/sem/tree,sql/coltypes: remove PGDisplayName r=knz a=knz

First commits from #28943 and priors.
Forked off #28690.

This an intermediate cleanup.

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

28945: sql: fix the reporting of types in information_schema.columns r=knz a=knz

First commits from #28944 and priors.
Forked off #28690.
Fixes #27601.
Largely addresses the concerns that led to issue #26925.

Prior to this patch, CockroachDB incorrectly placed the "input syntax"
of each SQL type in the column `data_type` of
`information_schema.columns`.

The input syntax is the one reported in SHOW COLUMNS, SHOW CREATE
TABLE and other places, and is suitable to reproduce the exact type of
at able.

In contrast, `information_schema.columns.data_type` is constrained by
compatibility with third party tools and PostgreSQL clients.  It must
report the name of the type like PostgreSQL does, which in turn is
constrained by the SQL standard. A text column must be reported as
"text" not "string"; a decimal column as "numeric" not "decimal", a
float8 column as "double precision" not "float8", and so on.

By reporting the wrong string in that column CockroachDB is confusing
ORMs, which subsequently decide that the current on-disk type is not
the one expected by the app and then initiate a schema change (ALTER
COLUMN SET TYPE).

This patch corrects this incompatibility by introducing logic that
produces the proper information schema names for column types. This is
expected to reduce ORM complaints about insufficient support for ALTER
COLUMN SET TYPE (but will be tested/evaluated separately).

Release note (bug fix): CockroachDB now populates the `data_type`
column of `information_schema.columns` like PostgreSQL for
compatibility with 3rd party tools and ORMs.

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

29006: backport-2.1: fix the handling of SQL types r=knz a=knz

Backport 1/1 commits from #28937.
Backport 1/1 commits from #28942.
Backport 17/17 commits from #28943.
Backport 1/1 commits from #28944.
Backport 1/1 commits from #28945.
Backport 1/1 commits from #28949.
Backport 2/2 commits from #28950.
Backport 1/1 commits from #28951 (#28959).
Backport 1/1 commits from #28952 (#28959).
Backport 1/1 commits from #28955 (#28959).
Backport 1/1 commits from #28959.
Backport 1/1 commits from #28959.
Backport 1/1 commits from #28690.

cc @cockroachdb/release 

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

29006: backport-2.1: fix the handling of SQL types r=knz a=knz

Backport 1/1 commits from #28937.
Backport 1/1 commits from #28942.
Backport 17/17 commits from #28943.
Backport 1/1 commits from #28944.
Backport 1/1 commits from #28945.
Backport 1/1 commits from #28949.
Backport 2/2 commits from #28950.
Backport 1/1 commits from #28951 (#28959).
Backport 1/1 commits from #28952 (#28959).
Backport 1/1 commits from #28955 (#28959).
Backport 1/1 commits from #28959.
Backport 1/1 commits from #28959.
Backport 1/1 commits from #28690.

cc @cockroachdb/release 

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