[jdk11u-dev] RFR: 8315731: Open source several Swing Text related tests

[Jonathan Dowland]

Test-only backport for Oracle parity. 5 newly-opensource Swing tests. Not clean: one required adjusting for JDK<14 (rework instanceof pattern matching). After that, they all pass for 11u.

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Commit messages:
 - Rework instanceof pattern matching from test (not in 11u)
 - 8315731: Open source several Swing Text related tests

Changes: https://git.openjdk.org/jdk11u-dev/pull/2434/files
 Webrev: https://webrevs.openjdk.org/?repo=jdk11u-dev&pr=2434&range=00
  Issue: https://bugs.openjdk.org/browse/JDK-8315731
  Stats: 469 lines in 5 files changed: 469 ins; 0 del; 0 mod
  Patch: https://git.openjdk.org/jdk11u-dev/pull/2434.diff
  Fetch: git fetch https://git.openjdk.org/jdk11u-dev.git pull/2434/head:pull/2434

PR: https://git.openjdk.org/jdk11u-dev/pull/2434