RFR: 8306055: Add a built-in Catalog to JDK XML module [v3]

[Joe Wang]

> Implement the built-in Catalog.

Joe Wang has updated the pull request incrementally with one additional commit since the last revision:

  add a note; fix alignment

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Changes:
  - all: https://git.openjdk.org/jdk/pull/16719/files
  - new: https://git.openjdk.org/jdk/pull/16719/files/c1059a84..4914278a

Webrevs:
 - full: https://webrevs.openjdk.org/?repo=jdk&pr=16719&range=02
 - incr: https://webrevs.openjdk.org/?repo=jdk&pr=16719&range=01-02

  Stats: 4 lines in 1 file changed: 0 ins; 0 del; 4 mod
  Patch: https://git.openjdk.org/jdk/pull/16719.diff
  Fetch: git fetch https://git.openjdk.org/jdk.git pull/16719/head:pull/16719

PR: https://git.openjdk.org/jdk/pull/16719