RFR: 8199149: Improve the exception message thrown by VarHandle of unsupported operation

[Mandy Chung]

`VarForm::getMemberName` currently throws UOE with no information if the requested access mode is unsupported.   To provide the var handle information, move the access mode check to `VarHandle` so that the exception message can include the var handle information.  Changes include:

1. change `VarHandle::checkAccessModeThenIsDirect` to check if the access mode is unsupported.  This check is only needed for direct var handle.
2. change `VarHandle::getMethodHandleUncached` to call `getMemberNameOrNull` and throw UOE with an informative exception message if the access mode is unsupported

The error message looks like:

java.lang.UnsupportedOperationException: compareAndSet is not supported for VarHandle[varType=java.lang.String, coord=[class Foo$Goo]]

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Commit messages:
 - 8199149: Improve the exception message thrown by VarHandle of unsupported operation

Changes: https://git.openjdk.org/jdk/pull/14928/files
 Webrev: https://webrevs.openjdk.org/?repo=jdk&pr=14928&range=00
  Issue: https://bugs.openjdk.org/browse/JDK-8199149
  Stats: 35 lines in 3 files changed: 31 ins; 0 del; 4 mod
  Patch: https://git.openjdk.org/jdk/pull/14928.diff
  Fetch: git fetch https://git.openjdk.org/jdk.git pull/14928/head:pull/14928

PR: https://git.openjdk.org/jdk/pull/14928