Various improvements (in particular a new painting fuzzer) to the text manual test.
Some additional documentation.
A fix to Stack to remove an LTR bias: make unpositioned children apply "alignment".
Some more debugging information on RichText and Text.
A fix to the flutter tool to not crash when an RPC call throws an exception.
Unlike FractionalOffset, Alignment uses the center as the zero of the
coordinate system, which makes the RTL math work out much cleaner.
Also, make FractionalOffset into a subclass of Alignment so that clients
can continue to use FractionalOffset.
This patch adds Positioned.directional and PositionedDirectional. The
former is useful when you already know the TextDirection. The latter is
useful when you want to use the ambeient Directionality.
Fixes#11390
Also:
* Add three explicit sizing modes to Stack for non-positioned
children: loose, expand, and passthrough. (All three are used.)
* Fix a bug whereby layers would try to paint in the same frame as
they were removed from layout (but not detached).
* Fix a bug whereby Offstage wasn't properly marking the parent dirty
when changing its sizedByParent flag.
* Explicitly make Overlay expand non-positioned children.
* Explicitly have InputDecoration pass through the constraints from
its Row to its Stack children.
