RFR: 8296660: Swing HTML table with omitted closing tags misparsed

[Prasanta Sadhukhan]

This is in continuation with https://github.com/openjdk/jdk/commit/7133fc93e168f3671d048b2ae654f84ec289b98d fix done for [JDK-7172359](https://bugs.openjdk.org/browse/JDK-7172359) issue where fix was done to rectify invalid tag causing StackOverflowError but it caused alignment issue if the closing tags are optional, so the fix is modified to check for optional closing tag in which case dont return false for legalElementContext()

JDK-7172359 fix and other CI regression tests are fine.

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Commit messages:
 - Fix
 - Fix
 - 8296660: Swing HTML table with omitted closing tags misparsed

Changes: https://git.openjdk.org/jdk/pull/11355/files
 Webrev: https://webrevs.openjdk.org/?repo=jdk&pr=11355&range=00
  Issue: https://bugs.openjdk.org/browse/JDK-8296660
  Stats: 74 lines in 2 files changed: 73 ins; 0 del; 1 mod
  Patch: https://git.openjdk.org/jdk/pull/11355.diff
  Fetch: git fetch https://git.openjdk.org/jdk pull/11355/head:pull/11355

PR: https://git.openjdk.org/jdk/pull/11355