RFR: 8371981: Wrong spit caret positioning with mixed text

[Andy Goryachev]

Fixing a silly mistake - mixed up `lineX2` and `lineY` parameters in `PrismTextLayout`.

-------------

Commit messages:
 - tests
 - fix

Changes: https://git.openjdk.org/jfx/pull/1976/files
  Webrev: https://webrevs.openjdk.org/?repo=jfx&pr=1976&range=00
  Issue: https://bugs.openjdk.org/browse/JDK-8371981
  Stats: 157 lines in 4 files changed: 152 ins; 5 del; 0 mod
  Patch: https://git.openjdk.org/jfx/pull/1976.diff
  Fetch: git fetch https://git.openjdk.org/jfx.git pull/1976/head:pull/1976

PR: https://git.openjdk.org/jfx/pull/1976