[jdk11u-dev] RFR: 8222669: Create and use new html.Entity class

[Amos Shi]

Backport of [JDK-8222669](https://bugs.openjdk.org/browse/JDK-8222669)

Testing
- Local: Test passed on `MacOS 14.4.1`
  - `dev-8222669-11/test/langtools/jdk/javadoc/doclet`: Test results: passed: 191
- Pipeline: 
- Testing Machine:

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Commit messages:
 - Backport 761466699c82aa45054b805d7177e8605651ec9d Manual merge
 - Backport 761466699c82aa45054b805d7177e8605651ec9d

Changes: https://git.openjdk.org/jdk11u-dev/pull/2680/files
  Webrev: https://webrevs.openjdk.org/?repo=jdk11u-dev&pr=2680&range=00
  Issue: https://bugs.openjdk.org/browse/JDK-8222669
  Stats: 362 lines in 32 files changed: 188 ins; 84 del; 90 mod
  Patch: https://git.openjdk.org/jdk11u-dev/pull/2680.diff
  Fetch: git fetch https://git.openjdk.org/jdk11u-dev.git pull/2680/head:pull/2680

PR: https://git.openjdk.org/jdk11u-dev/pull/2680