RFR: 8299756: Minor updates in CSS Reference

[Andy Goryachev]

Minor fixes and addition of missing sections:

- The 'system' font is missing from the list of generic font family names in the <font> section. ✓
- Explicitly add text color property -fx-fill to Text section, so as not to confuse with Labeled -fx-text-fill ✓
- TextFlow section is missing, properties: -fx-text-alignment, -fx-line-spacing, -fx-tab-size ✓
- Text: missing -fx-line-spacing, -fx-bounds-type ✓
- -fx-focus-traversable is in Node and not in Control (though there is some relevant comment) - keep as is. ✓
- Node: broken link to 'Control' (sic, not Controls) in "... see Controls for details" ✓
- Missing <text-bounds-type> type ✓

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Commit messages:
 - 8299756: Minor updates in CSS Reference

Changes: https://git.openjdk.org/jfx/pull/1144/files
 Webrev: https://webrevs.openjdk.org/?repo=jfx&pr=1144&range=00
  Issue: https://bugs.openjdk.org/browse/JDK-8299756
  Stats: 87 lines in 1 file changed: 84 ins; 0 del; 3 mod
  Patch: https://git.openjdk.org/jfx/pull/1144.diff
  Fetch: git fetch https://git.openjdk.org/jfx.git pull/1144/head:pull/1144

PR: https://git.openjdk.org/jfx/pull/1144