RFR: 8276670: G1: Rename G1CardSetFreePool and related classes [v2]

[Hamlin Li]

> As G1CardSetFreePool and related classes are going to be reused outside of the remembered set, they should be renamed.

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

  Albert review

-------------

Changes:
  - all: https://git.openjdk.java.net/jdk/pull/6514/files
  - new: https://git.openjdk.java.net/jdk/pull/6514/files/d2cd5c5d..3de196a5

Webrevs:
 - full: https://webrevs.openjdk.java.net/?repo=jdk&pr=6514&range=01
 - incr: https://webrevs.openjdk.java.net/?repo=jdk&pr=6514&range=00-01

  Stats: 12 lines in 7 files changed: 2 ins; 0 del; 10 mod
  Patch: https://git.openjdk.java.net/jdk/pull/6514.diff
  Fetch: git fetch https://git.openjdk.java.net/jdk pull/6514/head:pull/6514

PR: https://git.openjdk.java.net/jdk/pull/6514