RFR: 8254354: Add an asExact() VarHandle combinator [v2]

[Jorn Vernee]

> Hi,
> 
> This patch adds an asExact() combinator to VarHandle, that will return a new VarHandle that performs exact type checks, similar to MethodHandle::invokeExact, to help developers catch inexact VarHandle usage, which can lead to performance degradation.
> 
> This is implemented using a boolean flag in VarForm. If the flag is set, the exact type of the invocation is checked against the exact type in the VarForm. If there is a mismatch, a WrongMethodTypeException is thrown.
> 
> Thanks,
> Jorn

Jorn Vernee has updated the pull request incrementally with one additional commit since the last revision:

  Make internalName helper method static

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Changes:
  - all: https://git.openjdk.java.net/jdk/pull/843/files
  - new: https://git.openjdk.java.net/jdk/pull/843/files/65c5d145..dc1f9ecf

Webrevs:
 - full: https://webrevs.openjdk.java.net/?repo=jdk&pr=843&range=01
 - incr: https://webrevs.openjdk.java.net/?repo=jdk&pr=843&range=00-01

  Stats: 1 line in 1 file changed: 0 ins; 0 del; 1 mod
  Patch: https://git.openjdk.java.net/jdk/pull/843.diff
  Fetch: git fetch https://git.openjdk.java.net/jdk pull/843/head:pull/843

PR: https://git.openjdk.java.net/jdk/pull/843