Proved version of PROJ library PostGIS was compiled against

[strk]

Like we did for GEOS ( see #5306 ) it would be nice to also get information about PROJ version used at compile time.

It may help with the issues like #5741

[Sandro Santilli <strk@…>]

In 23a1dd0/git:

Drop code paths for PROJ version < 6.1.0, which is now required

Rework format of proj version string to follow GEOS approach

References #5742

[strk]

Ready for test: ​https://git.osgeo.org/gitea/postgis/postgis/pulls/206

[Sandro Santilli <strk@…>]

In bb94b8d/git:

New postgis_proj_compiled_version() and exposure in full version

Only shows compiled version in postgis_full_version() output
if it doesn't match with runtime version up to patchlevel.

Closes #5742