RFR: 8305898: Alternative self-forwarding mechanism

[Roman Kennke]

Currently, the Serial, Parallel and G1 GCs store a pointer to self into object headers to indicate promotion failure. This is problematic for compact object headers ([JDK-8294992](https://bugs.openjdk.org/browse/JDK-8294992)) because it would (temporarily) over-write the crucial class information, which we need for heap parsing. I would like to propose an alternative: use the currently unused 3rd header bit (previously biased-locking bit) to indicate that an object is 'self-forwarded'. That preserves the crucial class information in the upper bits of the header until the full header gets restored.

This is a trimmed-down/simplified version of the original proposal #13779:
 - It doesn't use/introduce any flags and avoids the associated branching.
 - It doesn't (need to) deal with displaced headers. (Current code would preserve header if necessary, Lilliput code would not use displaced headers and set the 3rd bit directly in existing header.)

Testing:
 - [x] hotspot_gc
 - [x] tier1
 - [x] tier2

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Commit messages:
 - 8305898: Alternative self-forwarding mechanism

Changes: https://git.openjdk.org/jdk/pull/17755/files
 Webrev: https://webrevs.openjdk.org/?repo=jdk&pr=17755&range=00
  Issue: https://bugs.openjdk.org/browse/JDK-8305898
  Stats: 55 lines in 8 files changed: 39 ins; 0 del; 16 mod
  Patch: https://git.openjdk.org/jdk/pull/17755.diff
  Fetch: git fetch https://git.openjdk.org/jdk.git pull/17755/head:pull/17755

PR: https://git.openjdk.org/jdk/pull/17755