RFR: JDK-8324182 Deprecate for removal SimpleSelector and CompoundSelector classes

[John Hendrikx]

The SimpleSelector and CompoundSelector classes are public classes in an exported package, javafx.css, but they are not intended to be used by applications. They are implementation details. They cannot be constructed directly and no other JavaFX API accepts or returns a SimpleSelector or CompoundSelector.

We should deprecate them for removal so we can move them to a non-exported package, removing them from the public API.

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Commit messages:
 - Deprecate for removal SimpleSelector and CompoundSelector

Changes: https://git.openjdk.org/jfx/pull/1340/files
 Webrev: https://webrevs.openjdk.org/?repo=jfx&pr=1340&range=00
  Issue: https://bugs.openjdk.org/browse/JDK-8324182
  Stats: 4 lines in 2 files changed: 4 ins; 0 del; 0 mod
  Patch: https://git.openjdk.org/jfx/pull/1340.diff
  Fetch: git fetch https://git.openjdk.org/jfx.git pull/1340/head:pull/1340

PR: https://git.openjdk.org/jfx/pull/1340