RFR: 8199149: Improve the exception message thrown by VarHandle of unsupported operation [v2]

[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]]

Mandy Chung has updated the pull request incrementally with one additional commit since the last revision:

  review feedback

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Changes:
  - all: https://git.openjdk.org/jdk/pull/14928/files
  - new: https://git.openjdk.org/jdk/pull/14928/files/cc66b08c..176df233

Webrevs:
 - full: https://webrevs.openjdk.org/?repo=jdk&pr=14928&range=01
 - incr: https://webrevs.openjdk.org/?repo=jdk&pr=14928&range=00-01

  Stats: 15 lines in 2 files changed: 0 ins; 11 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