build: Move loose scripts in meson subdir to tools

The build dir looks "prettier" without the meson subdir.
With prettier I mean: just the OSes subdirs.

libgimp/tests/meson.build

@@ -52,7 +52,7 @@ foreach test_name : tests
   custom_target(basename + '.dummy',
                 input: [ c_test_exe ],
                 output: [ basename + '.dummy' ],
-                command: [ python, meson.project_source_root() / 'build/meson/cp-plug-in-subfolder.py',
+                command: [ python, meson.project_source_root() / 'tools/cp-plug-in-subfolder.py',
                            c_test_exe, meson.current_build_dir() / 'c-tests' / basename,
                            '@OUTPUT@' ],
                 build_by_default: true,

meson.build

@@ -1229,7 +1229,7 @@ dbus_run_session = find_program('dbus-run-session', required: get_option('headle
 if xvfb_run.found() and dbus_run_session.found()
   conf.set('HAVE_XVFB_RUN', true)
   add_test_setup('headless',
-    exe_wrapper: find_program('build' / 'meson' / 'run_test_env.sh'),
+    exe_wrapper: find_program('tools' / 'run_test_env.sh'),
     is_default: true,
   )
 endif
@@ -1714,7 +1714,7 @@ if is_git_repository
   endif
 
   if git.found()
-    git_submodule_check = run_command(meson.project_source_root() / 'build/meson/check-gimp-data.py',
+    git_submodule_check = run_command(meson.project_source_root() / 'tools/check-gimp-data.py',
                                       check: false)
     if git_submodule_check.returncode() != 0
       submodule_warning = 'gimp-data submodule seems outdated. Possibly run from the source repository: git submodule update'

plug-ins/common/meson.build

@@ -252,7 +252,7 @@ foreach plugin : common_plugins_list
   plugin_custom_targets += custom_target('test-' + plugin_name,
                 input: [ plugin_exe ],
                 output: [ plugin_name + '.dummy' ],
-                command: [ python, meson.project_source_root() / 'build/meson/cp-plug-in-subfolder.py',
+                command: [ python, meson.project_source_root() / 'tools/cp-plug-in-subfolder.py',
                            plugin_exe, meson.current_build_dir() / 'test-plug-ins' / plugin_name,
                            '@OUTPUT@' ],
                 build_by_default: true)

plug-ins/python/meson.build

@@ -33,7 +33,7 @@ foreach plugin : python_plugins
     # from the build directory without installing it.
     # To be run even if we don't install Python plug-ins so that we can
     # still run them for in-build scripts.
-    run_command(python, meson.project_source_root() / 'build/meson/cp-plug-in-subfolder.py',
+    run_command(python, meson.project_source_root() / 'tools/cp-plug-in-subfolder.py',
                 meson.current_source_dir() / src, meson.current_build_dir() / name, check: true)
   endforeach
 endforeach