RFR: 8299576: Reimplement java.io.Bits using VarHandle access [v3]

[Per Minborg]

> Currently, `java.io.Bits` is using explicit logic to read/write various primitive types to/from byte arrays. Switching to the use of `VarHandle` access would provide better performance and less code. 
> 
> Also, using a standard API for these conversions means future `VarHandle` improvements will benefit `Bits` too. 
> 
> Improvements in `Bits` will propagate to `ObjectInputStream`, `ObjectOutputStream` and `RandomAccessFile`.
> 
> Initial benchmarks and performance discussions can be found here: https://github.com/openjdk/panama-foreign/pull/762

Per Minborg has updated the pull request incrementally with two additional commits since the last revision:

 - Improve test
 - Improve test

-------------

Changes:
  - all: https://git.openjdk.org/jdk/pull/11840/files
  - new: https://git.openjdk.org/jdk/pull/11840/files/13af8b6c..3a91f3e2

Webrevs:
 - full: https://webrevs.openjdk.org/?repo=jdk&pr=11840&range=02
 - incr: https://webrevs.openjdk.org/?repo=jdk&pr=11840&range=01-02

  Stats: 285 lines in 2 files changed: 113 ins; 127 del; 45 mod
  Patch: https://git.openjdk.org/jdk/pull/11840.diff
  Fetch: git fetch https://git.openjdk.org/jdk pull/11840/head:pull/11840

PR: https://git.openjdk.org/jdk/pull/11840