RFR: 8313743: Make fields final in sun.nio.ch [v3]

[Andrey Turbanov]

> Found a few fields in `sun.nio.ch` package which could be declared `final`.
> 
> Also I took oportunity to make a couple of cleanups:
> 1. Converted `sun.nio.ch.OptionKey` to a record. Getters naming are already match.
> 2. Removed `sun.nio.ch.WindowsAsynchronousSocketChannelImpl#addressSize`/`sun.nio.ch.WindowsSelectorImpl#addressSize` fields. Address size is already cached inside Unsafe (since [JDK-8221477](https://bugs.openjdk.org/browse/JDK-8221477)).

Andrey Turbanov has updated the pull request incrementally with one additional commit since the last revision:

  8313743: Make fields final in sun.nio.ch
  
  revert OptionKey back to regular class

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

Changes:
  - all: https://git.openjdk.org/jdk/pull/14980/files
  - new: https://git.openjdk.org/jdk/pull/14980/files/6f0b7596..dcbbd5d7

Webrevs:
 - full: https://webrevs.openjdk.org/?repo=jdk&pr=14980&range=02
 - incr: https://webrevs.openjdk.org/?repo=jdk&pr=14980&range=01-02

  Stats: 17 lines in 1 file changed: 16 ins; 0 del; 1 mod
  Patch: https://git.openjdk.org/jdk/pull/14980.diff
  Fetch: git fetch https://git.openjdk.org/jdk.git pull/14980/head:pull/14980

PR: https://git.openjdk.org/jdk/pull/14980