[jdk11u-dev] RFR: 8315889: Open source several Swing HTMLDocument related tests

[Amos Shi]

Backport of [JDK-8315889](https://bugs.openjdk.org/browse/JDK-8315889)

Testing
- Local: Test passed
  - `bug4226914.java`: Test results: passed: 1
  - `bug4251593.java`: Test results: passed: 1
  - `bug4687405.java`: Test results: passed: 1
  - `bug4213373.java`: Test results: passed: 1
- Pipeline: 
- Testing Machine:

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Commit messages:
 - Backport 8f46abc938ffe338e25d5fdbdcfa0aaa12edfa58

Changes: https://git.openjdk.org/jdk11u-dev/pull/2690/files
  Webrev: https://webrevs.openjdk.org/?repo=jdk11u-dev&pr=2690&range=00
  Issue: https://bugs.openjdk.org/browse/JDK-8315889
  Stats: 250 lines in 4 files changed: 250 ins; 0 del; 0 mod
  Patch: https://git.openjdk.org/jdk11u-dev/pull/2690.diff
  Fetch: git fetch https://git.openjdk.org/jdk11u-dev.git pull/2690/head:pull/2690

PR: https://git.openjdk.org/jdk11u-dev/pull/2690