pgsql: Make PG_TEST_EXTRA env var override the "meson setup" option

Make PG_TEST_EXTRA env var override the "meson setup" option

"meson test" used to ignore the PG_TEST_EXTRA environment variable,
which meant that in order to run additional tests, you had to run
"meson setup -DPG_TEST_EXTRA=...". That's somewhat expensive, and not
consistent with autoconf builds. Allow PG_TEST_EXTRA environment
variable to override the setup-time option at run time, so that you
can do "PG_TEST_EXTRA=... meson test".

To implement this, the configuration time value is passed as an extra
"--pg-test-extra" argument to testwrap instead of adding it to the
test environment. If the environment variable is set at the time of
running test, testwrap uses the value from the environment variable
and ignores the --pg-test-extra option.

Now that "meson test" obeys the environment variable, we can remove it
from the "meson setup" steps in the CI script. It will now be picked
up from the environment variable like with "make check".

Author: Nazir Bilal Yavuzk, Ashutosh Bapat
Reviewed-by: Ashutosh Bapat with inputs from Tom Lane and Andrew Dunstan

Branch
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master

Details
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https://git.postgresql.org/pg/commitdiff/3d1aec225ac4a1199079150dabfd0d34c5054127

Modified Files
--------------
.cirrus.tasks.yml | 6 +-----
doc/src/sgml/installation.sgml | 10 +++++++---
meson.build | 10 +++++-----
meson_options.txt | 2 +-
src/tools/testwrap | 10 ++++++++++
5 files changed, 24 insertions(+), 14 deletions(-)