* Back out code to generate mouse events on mutter. It had a couple of
  unwanted side effects. Also remove dependencies on libei and xkbcommon.

* atk-adaptor: Fix collection role matching.

* Have atspi_text_get_string_at_offset fall back to calling
  GetTextAtOffset if GetStringAtOffset is unimplemented.

* Don't use g_assert in the unit tests.

What's new in at-spi2-core 2.51.91: