<i18n dev> RFR: 8306597: Improve string formatting in EquivMapsGenerator.java

[Justin Lu]

Please review changes to `EquivMapsGenerator.java` (which is used to generate the Locale equivalencies for the JDK).

The file previously used large concatenated Strings, which are now replaced with text blocks, in addition to some cleanup. No functionality is changed, `EquivMapsGenerator.java` builds the same.

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Commit messages:
 - Replace ws with escaped newline
 - get rid of ws
 - Reduce duplication
 - Merge master and resolve conflicts
 - Reorder methods / text variables
 - Use Java text blocks and String format

Changes: https://git.openjdk.org/jdk/pull/13935/files
 Webrev: https://webrevs.openjdk.org/?repo=jdk&pr=13935&range=00
  Issue: https://bugs.openjdk.org/browse/JDK-8306597
  Stats: 164 lines in 1 file changed: 73 ins; 63 del; 28 mod
  Patch: https://git.openjdk.org/jdk/pull/13935.diff
  Fetch: git fetch https://git.openjdk.org/jdk.git pull/13935/head:pull/13935

PR: https://git.openjdk.org/jdk/pull/13935