Speculative fix for failing roll at https://github.com/flutter/engine/pull/24657

https://skia.googlesource.com/skia.git/+log/e79bb32365ea..4ac9aadd306b

2021-02-25 csmartdalton@google.com Make it possible to enable hw tessellation outside of test builds
2021-02-25 mtklein@google.com Revert "Remove CapsMap from IR Generator."
2021-02-25 fmalita@google.com Revert "Add DSL PossibleExpression & PossibleStatement"
2021-02-25 fmalita@google.com Revert "SkSL DSL now reports the C++ line numbers of errors"

If this roll has caused a breakage, revert this CL and stop the roller
using the controls here:
https://autoroll.skia.org/r/skia-flutter-autoroll
Please CC fmalita@google.com on the revert to ensure that a human
is aware of the problem.

To report a problem with the AutoRoller itself, please file a bug:
https://bugs.chromium.org/p/skia/issues/entry?template=Autoroller+Bug

Documentation for the AutoRoller is here:
https://skia.googlesource.com/buildbot/+doc/master/autoroll/README.md

[macos] Reland default metal and also check if the system supports metal before defaulting to it (#24601)

This replaces the custom Obj-C TextInputModel implementation used on
macOS with the common C++ implementation used on Linux and Windows. Note
that as a side-effect, this change enables *some* direct IME input for
CJK input but full input will land in follow-up patches that land:

1. Add handling for TextInput.setMarkedTextRect message
2. Add handling for TextInput.setEditableSizeAndTransform message
3. Implement firstRectForCharacterRange:actualRange: using the above.
4. Add NSTextInputContext handling.