RFR: 8301220: Return value of toArray() of Сollection types from java.base should be trusted

[Glavo]

I checked the `java.base` module, and all the `Collection#toArray()` method of collections be implemented correctly.

Their return values can be trusted, so many unnecessary array duplication can be eliminated.

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Commit messages:
 - fix checkstyle
 - Update ImmutableCollections
 - Merge branch 'master' into array-copy
 - Rollback Collectors
 - fix checkstyle
 - update
 - Update List.copyOf
 - Return value of toArray of collection types in java.base should be trusted

Changes: https://git.openjdk.org/jdk/pull/12212/files
 Webrev: https://webrevs.openjdk.org/?repo=jdk&pr=12212&range=00
  Issue: https://bugs.openjdk.org/browse/JDK-8301220
  Stats: 14 lines in 6 files changed: 2 ins; 2 del; 10 mod
  Patch: https://git.openjdk.org/jdk/pull/12212.diff
  Fetch: git fetch https://git.openjdk.org/jdk pull/12212/head:pull/12212

PR: https://git.openjdk.org/jdk/pull/12212