RFR: 8342565: [TestBug] StubTextLayout

[Andy Goryachev]

Changed the StubTextLayout to use product PrismTextLayout with much simplified glyph layout (via stubbed fonts).  The new layout assumes all the glyphs are squares of font size, while the bold type face produces wider glyphs (by 1 pixel).  The default font size has changed from 10 to 12 to make it closer to win/linux.

This brings the test environment closer to the product configuration and expands the capabilities of our headless testing pipeline, which will be useful for upcoming behavior tests.

Existing tests have been adjusted/reworked mainly due to default font size change.

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Commit messages:
 - cleanup
 - better test
 - cleanup
 - more magic
 - magic numbers
 - more
 - add exports
 - stub fonts
 - glyph run
 - truncated
 - ... and 7 more: https://git.openjdk.org/jfx/compare/f2f5639c...a4a3ebb3

Changes: https://git.openjdk.org/jfx/pull/1667/files
  Webrev: https://webrevs.openjdk.org/?repo=jfx&pr=1667&range=00
  Issue: https://bugs.openjdk.org/browse/JDK-8342565
  Stats: 1168 lines in 35 files changed: 692 ins; 270 del; 206 mod
  Patch: https://git.openjdk.org/jfx/pull/1667.diff
  Fetch: git fetch https://git.openjdk.org/jfx.git pull/1667/head:pull/1667

PR: https://git.openjdk.org/jfx/pull/1667