RFR: 8258032: Reconsider LEAF entry restrictions [v2]

[Coleen Phillimore]

> This change allows JRT_LEAF functions to create Handles because it doesn't need them but some code inside the VM needs Handles.  There's a NoSafepointVerifier in JRT_LEAF functions.
> The JNI_LEAF and JVM_LEAF functions have NoHandleMark (so you can't create handles) but the transition ThreadInVMfromNative will reenable the HandleMarks, so that all this code doesn't have to do it itself.
> Tested with tier1-6.

Coleen Phillimore has updated the pull request incrementally with one additional commit since the last revision:

  Fix copyrights.

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Changes:
  - all: https://git.openjdk.java.net/jdk/pull/1846/files
  - new: https://git.openjdk.java.net/jdk/pull/1846/files/3b4a1750..6f65664f

Webrevs:
 - full: https://webrevs.openjdk.java.net/?repo=jdk&pr=1846&range=01
 - incr: https://webrevs.openjdk.java.net/?repo=jdk&pr=1846&range=00-01

  Stats: 16 lines in 16 files changed: 0 ins; 0 del; 16 mod
  Patch: https://git.openjdk.java.net/jdk/pull/1846.diff
  Fetch: git fetch https://git.openjdk.java.net/jdk pull/1846/head:pull/1846

PR: https://git.openjdk.java.net/jdk/pull/1846