<i18n dev> RFR: 8303039: Utilize `coverageLevels.txt`

[Naoto Sato]

This is a pre-requisite for supporting CLDR v43, where they combine `seeds` locales with `common` locales (https://cldr.unicode.org/index/downloads/cldr-43#h.7s25aqdv767e). In order to have the same coverage level of locales, CLDRConverter tool needs to comb through the locale files based on the `coverageLevels.txt` file, (and the ones we already included as of v42). Confirmed the same set of locales is generated before and after this modification.

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Commit messages:
 - 8303039: Utilize `coverageLevels.txt`

Changes: https://git.openjdk.org/jdk/pull/12812/files
 Webrev: https://webrevs.openjdk.org/?repo=jdk&pr=12812&range=00
  Issue: https://bugs.openjdk.org/browse/JDK-8303039
  Stats: 318 lines in 4 files changed: 314 ins; 1 del; 3 mod
  Patch: https://git.openjdk.org/jdk/pull/12812.diff
  Fetch: git fetch https://git.openjdk.org/jdk pull/12812/head:pull/12812

PR: https://git.openjdk.org/jdk/pull/12812