RFR: 8282209: G1: Use synchronous concurrent marking for the code cache [v2]

[Leo Korinth]

> This fix removes collect_for_codecache(), and uses collect() directly instead. This has the advantage that the g1 code path can be run concurrently using a concurrent mark instead of a full gc.

Leo Korinth has updated the pull request incrementally with one additional commit since the last revision:

  extract static method, and fixup comment

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Changes:
  - all: https://git.openjdk.java.net/loom/pull/102/files
  - new: https://git.openjdk.java.net/loom/pull/102/files/7c1a6c78..fc2b3863

Webrevs:
 - full: https://webrevs.openjdk.java.net/?repo=loom&pr=102&range=01
 - incr: https://webrevs.openjdk.java.net/?repo=loom&pr=102&range=00-01

  Stats: 35 lines in 5 files changed: 13 ins; 17 del; 5 mod
  Patch: https://git.openjdk.java.net/loom/pull/102.diff
  Fetch: git fetch https://git.openjdk.java.net/loom pull/102/head:pull/102

PR: https://git.openjdk.java.net/loom/pull/102