RFR: 8317228: GC: Make TestXXXHeapSizeFlags use createTestJvm [v4]

[Leo Korinth]

> Minor testing done, I will test more later with other fixes.

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

  add flag-sensitive key to TEST.ROOT

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Changes:
  - all: https://git.openjdk.org/jdk/pull/15986/files
  - new: https://git.openjdk.org/jdk/pull/15986/files/f0aaa67f..a5b87914

Webrevs:
 - full: https://webrevs.openjdk.org/?repo=jdk&pr=15986&range=03
 - incr: https://webrevs.openjdk.org/?repo=jdk&pr=15986&range=02-03

  Stats: 1 line in 1 file changed: 0 ins; 0 del; 1 mod
  Patch: https://git.openjdk.org/jdk/pull/15986.diff
  Fetch: git fetch https://git.openjdk.org/jdk.git pull/15986/head:pull/15986

PR: https://git.openjdk.org/jdk/pull/15986