RFR: Freeze functions [v10]

[Robbin Ehn]

> Freeze functions

Robbin Ehn has updated the pull request with a new target base due to a merge or a rebase. The pull request now contains three commits:

 - Freeze funcs
 - Change HeapMonitorVMEventsTest to not enable preview when virtual threads are unused
 - StackChunk only special in null loader.
   
   Reviewed-by: rpressler, stefank, eosterlund

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Changes: https://git.openjdk.java.net/loom/pull/156/files
 Webrev: https://webrevs.openjdk.java.net/?repo=loom&pr=156&range=09
  Stats: 398 lines in 6 files changed: 226 ins; 85 del; 87 mod
  Patch: https://git.openjdk.java.net/loom/pull/156.diff
  Fetch: git fetch https://git.openjdk.java.net/loom pull/156/head:pull/156

PR: https://git.openjdk.java.net/loom/pull/156