RFR: 8276824: refactor Thread::is_JavaThread_protected

[Daniel D.Daugherty]

Refactor `Thread::is_JavaThread_protected(const JavaThread* p, bool checkTLHOnly)`
into: `bool Thread::is_JavaThread_protected(const JavaThread* p)`
and: `Thread::is_JavaThread_protected_by_TLH(const JavaThread* p)`.
Also change callers that passed `checkTLHOnly == true` into calls to
`Thread::is_JavaThread_protected_by_TLH(const JavaThread* p)`.

This refactoring is being tested with Mach5 Tier[1-3] (in process).

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Commit messages:
 - 8276824.cr0.patch

Changes: https://git.openjdk.java.net/jdk/pull/6315/files
 Webrev: https://webrevs.openjdk.java.net/?repo=jdk&pr=6315&range=00
  Issue: https://bugs.openjdk.java.net/browse/JDK-8276824
  Stats: 80 lines in 3 files changed: 34 ins; 22 del; 24 mod
  Patch: https://git.openjdk.java.net/jdk/pull/6315.diff
  Fetch: git fetch https://git.openjdk.java.net/jdk pull/6315/head:pull/6315

PR: https://git.openjdk.java.net/jdk/pull/6315