RFR: 8319324: FFM: Reformat javadocs [v3]

[Per Minborg]

> This PR proposes to reformat all the JavaDocs for the FFM API. This would bring the FFM API docs more in line with the existing Java documentation (see below).  Occasional drive-by fixes are also included in this PR (such as spelling and capitalization).
> 
> I am aware this PR will (if approved) make a significant mark in the change logs which is regrettable.
> 
> Background:
> 
> Older classes like `Object` and `List` have a maximum line length of 80 characters whereas newer classes like `ScopedValue` have a maximum line length of 90 characters.
> 
> The FFM API currently has javadoc lines that exceed 135 characters per line. It is also customary to use double spaces when starting a new sentence.

Per Minborg has updated the pull request incrementally with one additional commit since the last revision:

  Update after review

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

Changes:
  - all: https://git.openjdk.org/jdk/pull/16518/files
  - new: https://git.openjdk.org/jdk/pull/16518/files/d0fddb0f..0c379b4a

Webrevs:
 - full: https://webrevs.openjdk.org/?repo=jdk&pr=16518&range=02
 - incr: https://webrevs.openjdk.org/?repo=jdk&pr=16518&range=01-02

  Stats: 15 lines in 2 files changed: 10 ins; 1 del; 4 mod
  Patch: https://git.openjdk.org/jdk/pull/16518.diff
  Fetch: git fetch https://git.openjdk.org/jdk.git pull/16518/head:pull/16518

PR: https://git.openjdk.org/jdk/pull/16518