meson: debug messages of libgdata don't come from correct log domain - "libgdata"

When we link GVfs against the libgdata (after the meson port) and try to print the debug output, all of libgdata's debug output gets prefixed with domain - google-drive:. Moreover, with autotools, we had a separate log domain for each of the demo we had. The G_LOG_DOMAIN needs to be fixed for the shared_library as well as executable.