Move locale migration after cleanup

[chrisawi]

Otherwise, module-level cleanup can remove locale symlinks that point to locale data installed by other modules.

Closes #154

I've tested this building an app, and for that at least, it seems to work. I haven't tried building a runtime though. There are two other calls to builder_migrate_locale_dirs() that I haven't really investigated. One happens in init for all runtimes, and the other applies only to platforms.

[TingPing]

If you could, add some tests to https://github.com/flatpak/flatpak-builder/blob/main/tests/test-builder.sh

[bbhtt]

The other two calls should be unaffected by the bug.

The first one happens when build-runtime: true and init runs. That's already before any module have been built and just sets up the locale dir structure for the runtime pre-build.

The next call happens when creating the platform-base which is already after cleanup phase has run

flatpak-builder/src/builder-main.c

Lines 1036 to 1052 in 9ea44e0

	if (!builder_manifest_cleanup (manifest, cache, build_context, &error))
	{
	g_printerr ("Error: %s\n", error->message);
	return 1;
	}
	if (!builder_manifest_finish (manifest, cache, build_context, &error))
	{
	g_printerr ("Error: %s\n", error->message);
	return 1;
	}
	if (!builder_manifest_create_platform (manifest, cache, build_context, &error))
	{
	g_printerr ("Error: %s\n", error->message);
	return 1;
	}