RFR: 8307547: Support for multiple collations for a locale

Wed May 10 20:19:59 UTC 2023

The fix to https://bugs.openjdk.org/browse/JDK-8306927 switched the default collation for Swedish to the modern one. In order to provide a means for users who need the old collation, this PR intends to make `Collator` recognize the `co` Unicode locale extension so that multiple implementations for a locale can be provided. I would also like reviews for the corresponding CSR.

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Commit messages:
 - Test refinement
 - Clean-up
 - javadoc
 - 8307547: Support for multiple collation tables

Changes: https://git.openjdk.org/jdk/pull/13917/files
 Webrev: https://webrevs.openjdk.org/?repo=jdk&pr=13917&range=00
  Issue: https://bugs.openjdk.org/browse/JDK-8307547
  Stats: 71 lines in 4 files changed: 57 ins; 4 del; 10 mod
  Patch: https://git.openjdk.org/jdk/pull/13917.diff
  Fetch: git fetch https://git.openjdk.org/jdk.git pull/13917/head:pull/13917

PR: https://git.openjdk.org/jdk/pull/13917