clutter test: add Clutter::Actor tests

Hmm,... Clutter::Actor transform series methods requires Cogl::Matrix(Clutter::Matrix).
But, we don't have this. :<
clutter test: add Clutter::Actor margin tests
clutter: always require pango

Because Clutter::Actor#create_pango_context returns Pango::Context.
And it needs its test.
clutter test: fix test_pango_context to use assert_kind_of