Fixes a crash when releasing a property that was not retained before. Helps: https://gitlab.gnome.org/GNOME/glib/issues/1751
This reverts commit 2e9f3a9afe4c5cb1ebdda5e33e6fd3552bf56d38.
This reverts commit e400af99d436b003b93479e4892623f336f58a6b.
Those files got renamed to .c to work around an automake issue, but Meson needs them to have .m extension. Better rename them at build time in Makefile.am since that's where the workaround is needed. https://bugzilla.gnome.org/show_bug.cgi?id=672777