RFR: 8276670: G1: Move and rename G1CardSetFreePool and related classes [v3]

[Hamlin Li]

> This is to simply move and rename G1CardSetFreePool and related classes, as G1CardSetFreePool and related classes are going to be reused outside of the remembered set, they should be factored out and renamed.
> Rename from G1CardSetXxx -> G1BufferListXxx.

Hamlin Li has updated the pull request incrementally with one additional commit since the last revision:

  Fix typo

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Changes:
  - all: https://git.openjdk.java.net/jdk/pull/6289/files
  - new: https://git.openjdk.java.net/jdk/pull/6289/files/02c2b940..c15129e4

Webrevs:
 - full: https://webrevs.openjdk.java.net/?repo=jdk&pr=6289&range=02
 - incr: https://webrevs.openjdk.java.net/?repo=jdk&pr=6289&range=01-02

  Stats: 4 lines in 1 file changed: 0 ins; 0 del; 4 mod
  Patch: https://git.openjdk.java.net/jdk/pull/6289.diff
  Fetch: git fetch https://git.openjdk.java.net/jdk pull/6289/head:pull/6289

PR: https://git.openjdk.java.net/jdk/pull/6289