RFR: 8290844: Add Skin.install() method [v3]

[Andy Goryachev]

> - added Skin.install()
> - javadoc changes for Skinnable.setSkin(Skin)
> 
> no code changes for Skinnable.setSkin(Skin) yet.

Andy Goryachev has updated the pull request with a new target base due to a merge or a rebase. The incremental webrev excludes the unrelated changes brought in by the merge/rebase. The pull request contains 13 additional commits since the last revision:

 - 8290844: review comments
 - Merge remote-tracking branch 'origin/master' into 8290844.skin.install
 - 8290844: javadoc
 - Merge remote-tracking branch 'origin/master' into 8290844.skin.install
 - 8289397: added space
 - 8290844: skin.install
 - 8290844: whitespace
 - 8290844: validate input
 - 8290844: illegal argument exception
 - 8290844: illegal argument exception
 - ... and 3 more: https://git.openjdk.org/jfx/compare/bcd10d1b...647ecd6c

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

Changes:
  - all: https://git.openjdk.org/jfx/pull/845/files
  - new: https://git.openjdk.org/jfx/pull/845/files/cfa99760..647ecd6c

Webrevs:
 - full: https://webrevs.openjdk.org/?repo=jfx&pr=845&range=02
 - incr: https://webrevs.openjdk.org/?repo=jfx&pr=845&range=01-02

  Stats: 447938 lines in 7521 files changed: 301334 ins; 103537 del; 43067 mod
  Patch: https://git.openjdk.org/jfx/pull/845.diff
  Fetch: git fetch https://git.openjdk.org/jfx pull/845/head:pull/845

PR: https://git.openjdk.org/jfx/pull/845