libui: PrintTo and comparisons for values for tests

Define `PrintTo` and (except for Region) ensure there is an appropriate
`operator==`. The Google Test framework will uses `PrintTo` to print out
values if available, and uses operator == to check if values match
expected values.

The following value types were modified:

  * Rect
  * FloatRect
  * Region
  * Transform

With these definitions, the Composition Engine tests no longer need
custom matchers to print/compare values (except for Region).

For Region it seemed unwise to define a general `operator==` as equality
of Regions might mean different things to different callers. Instead
this change just adds a `Region::hasSameRects(const Region& other)`
function to do the fast check that the tests were doing. As such a
matcher helper is still needed which calls that function, though now it
is much more trivial to write.

Bug: None
Test: libcompositionengine_test
Change-Id: I160cda695d99257966634e767ee1164bc6105e30