Enable Python Limited API for PL/Python on MSVC

Activate Python "Limited API" in PL/Python

Prepare for Python "Limited API" in PL/Python

Remove obsolete Python version check

doc PG 18 relnotes: Add migration note about tsearch

Remove ts_locale.c's lowerstr()

Remove ts_locale.c's t_isdigit(), t_isspace(), t_isprint()

oauth: Correct test dependency on oauth_hook_client

meson: Add pg_regress_ecpg to ecpg test dependencies

meson: Improve dependencies for tmp_install test target

meson: Narrow dependencies for 'install-quiet' target

meson: Add missing dependencies for libpq tests

Return yyparse() result not via global variable

Remove flex version checks

Drop warning-free support for Flex 2.5.35

plpgsql: pure parser and reentrant scanner

flex code modernization: Replace YY_EXTRA_TYPE define with flex option