RFR: 8143041: Unify G1CollectorPolicy::PauseKind and G1YCType [v3]

[Ivan Walulya]

> Please review this refactoring change to unify G1CollectorPolicy::PauseKind and G1YCType enums under the same file. Additionally, make the distinction between collector types and phases clearer.

Ivan Walulya has updated the pull request incrementally with one additional commit since the last revision:

  refactor after Thomas review

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Changes:
  - all: https://git.openjdk.java.net/jdk/pull/2870/files
  - new: https://git.openjdk.java.net/jdk/pull/2870/files/0ba80797..14fda964

Webrevs:
 - full: https://webrevs.openjdk.java.net/?repo=jdk&pr=2870&range=02
 - incr: https://webrevs.openjdk.java.net/?repo=jdk&pr=2870&range=01-02

  Stats: 1 line in 1 file changed: 1 ins; 0 del; 0 mod
  Patch: https://git.openjdk.java.net/jdk/pull/2870.diff
  Fetch: git fetch https://git.openjdk.java.net/jdk pull/2870/head:pull/2870

PR: https://git.openjdk.java.net/jdk/pull/2870