RFR: 8317755: G1: Periodic GC interval should test for the last whole heap GC [v3]

[Aleksey Shipilev]

> See the description in the bug. Fortunately, we already track the last whole-heap GC. The new regression test verifies the behavior.
> 
> Additional testing:
>  - [x] Linux x86_64 fastdebug `tier1 tier2 tier3`

Aleksey Shipilev has updated the pull request with a new target base due to a merge or a rebase. The incremental webrev excludes the unrelated changes brought in by the merge/rebase. The pull request contains six additional commits since the last revision:

 - Merge branch 'master' into JDK-8317755-g1-periodic-whole
 - Merge branch 'master' into JDK-8317755-g1-periodic-whole
 - Optional flag
 - Merge branch 'master' into JDK-8317755-g1-periodic-whole
 - Keep the cast
 - Fix

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

Changes:
  - all: https://git.openjdk.org/jdk/pull/16107/files
  - new: https://git.openjdk.org/jdk/pull/16107/files/4025fd02..145e96b2

Webrevs:
 - full: https://webrevs.openjdk.org/?repo=jdk&pr=16107&range=02
 - incr: https://webrevs.openjdk.org/?repo=jdk&pr=16107&range=01-02

  Stats: 714801 lines in 3525 files changed: 137625 ins; 497951 del; 79225 mod
  Patch: https://git.openjdk.org/jdk/pull/16107.diff
  Fetch: git fetch https://git.openjdk.org/jdk.git pull/16107/head:pull/16107

PR: https://git.openjdk.org/jdk/pull/16107