RFR: 8300891: Deprecate for removal javax.swing.plaf.synth.SynthLookAndFeel.load(URL url) [v4]

[Phil Race]

> SynthLookAndFeel.load(URL) is problematic because applications need to trust the URL.
> As documented in the bug report there are alternative mechanisms and JDK itself has not used this for the two Synth based L&Fs : Nimbus and GTK.
> So deprecating - for removal - and adding warnings now in the docs is appropriate.

Phil Race has updated the pull request incrementally with one additional commit since the last revision:

  8300891

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

Changes:
  - all: https://git.openjdk.org/jdk/pull/12175/files
  - new: https://git.openjdk.org/jdk/pull/12175/files/a9d49aa3..6a0131bd

Webrevs:
 - full: https://webrevs.openjdk.org/?repo=jdk&pr=12175&range=03
 - incr: https://webrevs.openjdk.org/?repo=jdk&pr=12175&range=02-03

  Stats: 9 lines in 1 file changed: 3 ins; 0 del; 6 mod
  Patch: https://git.openjdk.org/jdk/pull/12175.diff
  Fetch: git fetch https://git.openjdk.org/jdk pull/12175/head:pull/12175

PR: https://git.openjdk.org/jdk/pull/12175