[jdk21u-dev] RFR: 8326734: text-decoration applied to <span> lost when mixed with <u> or <s>

[Martin Doerr]

Clean backport of [JDK-8326734](https://bugs.openjdk.org/browse/JDK-8326734) and [JDK-8325620](https://bugs.openjdk.org/browse/JDK-8325620) which belong together.

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Commit messages:
 - Backport cd3e4c03661f770ebeefcd3637d56589243ac0a9

Changes: https://git.openjdk.org/jdk21u-dev/pull/664/files
  Webrev: https://webrevs.openjdk.org/?repo=jdk21u-dev&pr=664&range=00
  Issue: https://bugs.openjdk.org/browse/JDK-8326734
  Stats: 595 lines in 8 files changed: 539 ins; 32 del; 24 mod
  Patch: https://git.openjdk.org/jdk21u-dev/pull/664.diff
  Fetch: git fetch https://git.openjdk.org/jdk21u-dev.git pull/664/head:pull/664

PR: https://git.openjdk.org/jdk21u-dev/pull/664