RFR: JDK-8304959: Public API in javafx.css.Match should not return private API class PseudoClassState [v9]

[John Hendrikx]

> The class `PseudoClassState` is private API, but was exposed erroneously in the CSS API. Instead, `Set<PseudoClass>` should have been used. This PR corrects this.

John Hendrikx has refreshed the contents of this pull request, and previous commits have been removed. The incremental views will show differences compared to the previous content of the PR. The pull request contains three new commits since the last revision:

 - Add tests from #1076
 - Merge remote-tracking branch 'upstream/master' into feature/remove-private-api-in-css
 - Fix possible regression

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Changes:
  - all: https://git.openjdk.org/jfx/pull/1070/files
  - new: https://git.openjdk.org/jfx/pull/1070/files/80ff9992..da8ac037

Webrevs:
 - full: https://webrevs.openjdk.org/?repo=jfx&pr=1070&range=08
 - incr: https://webrevs.openjdk.org/?repo=jfx&pr=1070&range=07-08

  Stats: 43 lines in 2 files changed: 41 ins; 0 del; 2 mod
  Patch: https://git.openjdk.org/jfx/pull/1070.diff
  Fetch: git fetch https://git.openjdk.org/jfx.git pull/1070/head:pull/1070

PR: https://git.openjdk.org/jfx/pull/1070