pgsql: Move isolation test index-killtuples to src/test/modules/index/

Move isolation test index-killtuples to src/test/modules/index/

index-killtuples test depends on the contrib modules btree_gin and
btree_gist, which would not be installed in a temporary installation
with an execution of the main isolation test suite like this one:
make -C src/test/isolation/ check

src/test/isolation/ should not depend on contrib/, and EXTRA_INSTALL has
no effect in this case as this test suite uses its own Makefile rules.

This commit moves index-killtuples into its new module, called "index",
whose name looks like the best fit there can be as it depends on more
than one index AM. btree_gin and btree_gist are now pulled in the
temporary installation with EXTRA_INSTALL. The test is renamed to
"killtuples", for simplicity.

Author: Nazir Bilal Yavuz <byavuz81(at)gmail(dot)com>
Suggested-by: Andres Freund <andres(at)anarazel(dot)de>
Suggested-by: Michael Paquier <michael(at)paquier(dot)xyz>
Discussion: https://postgr.es/m/aKJsWedftW7UX1WM@paquier.xyz

Branch
------
master

Details
-------
https://git.postgresql.org/pg/commitdiff/e429c3cecb4ac55d997acea0f76c5f06d6cb0ab3

Modified Files
--------------
src/test/isolation/isolation_schedule | 1 -
src/test/modules/Makefile | 1 +
src/test/modules/index/.gitignore | 6 ++++++
src/test/modules/index/Makefile | 16 ++++++++++++++++
.../index/expected/killtuples.out} | 0
src/test/modules/index/meson.build | 12 ++++++++++++
.../index/specs/killtuples.spec} | 0
src/test/modules/meson.build | 1 +
8 files changed, 36 insertions(+), 1 deletion(-)