meson: Narrow dependencies for 'install-quiet' target

Previously test dependencies, which are not actually installed, were
unnecessarily built.

Apply this to all branches with meson support, as part of an effort to fix
incorrect test dependencies that can lead to test failures.

Discussion: https://postgr.es/m/CAGECzQSvM3iSDmjF+=Kof5an6jN8UbkP_4cKKT9w6GZavmb5yQ@mail.gmail.com
Discussion: https://postgr.es/m/bdba588f-69a9-4f3e-9b95-62d07210a32e@eisentraut.org
Backpatch: 16-, where meson support was added

meson.build

@@ -3239,24 +3239,30 @@ if libintl.found() and meson.version().version_compare('>=0.60')
 endif
 
 
-all_built = [
+# all targets that 'meson install' needs
+installed_targets = [
   backend_targets,
   bin_targets,
   libpq_st,
   pl_targets,
   contrib_targets,
   nls_mo_targets,
-  testprep_targets,
   ecpg_targets,
 ]
 
+# all targets that require building code
+all_built = [
+  installed_targets,
+  testprep_targets,
+]
+
 # Meson's default install target is quite verbose. Provide one that is quiet.
 install_quiet = custom_target('install-quiet',
   output: 'install-quiet',
   build_always_stale: true,
   build_by_default: false,
   command: [meson_bin, meson_args, 'install', '--quiet', '--no-rebuild'],
-  depends: all_built,
+  depends: installed_targets,
 )
 
 # Target to install files used for tests, which aren't installed by default