[jdk21u-dev] RFR: 8325613: CTW: Stale method cleanup requires GC after Sweeper removal

[Aleksey Shipilev]

Clean backport to improve CTW testing times.

Additional testing:
 - [x] Ad-hoc CTW time measurements for `java.base` demonstrate the same improvements as in mainline
 - [x] Linux x86_64 server fastdebug, large CTW runs pass with this patch applied
 - [x] MacOS AArch64 server fastdebug, `applications/ctw/modules` passes

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Commit messages:
 - Backport 1281e18f1447848d7eb5e3bde508ac002b4c390d

Changes: https://git.openjdk.org/jdk21u-dev/pull/370/files
  Webrev: https://webrevs.openjdk.org/?repo=jdk21u-dev&pr=370&range=00
  Issue: https://bugs.openjdk.org/browse/JDK-8325613
  Stats: 26 lines in 2 files changed: 24 ins; 1 del; 1 mod
  Patch: https://git.openjdk.org/jdk21u-dev/pull/370.diff
  Fetch: git fetch https://git.openjdk.org/jdk21u-dev.git pull/370/head:pull/370

PR: https://git.openjdk.org/jdk21u-dev/pull/370