RFR: 8258032: Reconsider LEAF entry restrictions

[Coleen Phillimore]

Please review the smaller version of this enhancement.  JRT_LEAF can allow Handles.  Fixed places where a ResetNoHandleMark was added to workaround the restriction and remove some obsolete comments in deoptimization (the function is a JRT_BLOCK_ENTRY that has a HandleMarkCleaner which cleans up the HandleMark to the one before call_stub() in JavaCalls. A HandleMarkCleaner also allows HandleMark and Handles.

Tested with tier1-3, 4-6 with the larger change and 7-8 in progress.

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Commit messages:
 - Remove slow_identity_hash ResetNoHandleMark
 - 8258032: Reconsider LEAF entry restrictions

Changes: https://git.openjdk.java.net/jdk/pull/1990/files
 Webrev: https://webrevs.openjdk.java.net/?repo=jdk&pr=1990&range=00
  Issue: https://bugs.openjdk.java.net/browse/JDK-8258032
  Stats: 23 lines in 5 files changed: 3 ins; 16 del; 4 mod
  Patch: https://git.openjdk.java.net/jdk/pull/1990.diff
  Fetch: git fetch https://git.openjdk.java.net/jdk pull/1990/head:pull/1990

PR: https://git.openjdk.java.net/jdk/pull/1990