RFR: 8292948: JEditorPane ignores font-size styles in external linked css-file

[Stanimir Stamenkov]

[JDK-8292948] reveals a regression by the fix for [JDK-8257664] (#1759) causing `font-size` declarations from external style sheets to be ignored.

As far as I've traced, the problem is with the `isDefined(CSS.Attribute.FONT_SIZE)` test:

https://github.com/openjdk/jdk/blob/70b5b3119b2ed032b021a080f34a4fa28d092fb5/src/java.desktop/share/classes/javax/swing/text/html/StyleSheet.java#L2825-L2830

It misses declarations from linked styles via a `resolver` ([`AttributeSet.ResolveAttribute`](https://github.com/openjdk/jdk/blob/b0e0b87891eb81c2b33c1cfa598701b7bd2e5bdf/src/java.desktop/share/classes/javax/swing/text/AttributeSet.java#L187-L191)) attribute that happens to hold the external style sheet rules.  The fix for this would be to move the implied `CSS.Attribute.FONT_SIZE` handling after:

https://github.com/openjdk/jdk/blob/70b5b3119b2ed032b021a080f34a4fa28d092fb5/src/java.desktop/share/classes/javax/swing/text/html/StyleSheet.java#L2833-L2835

and drop the `isDefined()` test.

[I'll prepare a jtreg test further.]

[JDK-8292948]: https://bugs.openjdk.org/browse/JDK-8292948 "JEditorPane ignores font-size styles in external linked css-file"
[JDK-8257664]: https://bugs.openjdk.org/browse/JDK-8257664 "HTMLEditorKit: Wrong CSS relative font sizes"

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Commit messages:
 - 8292948: Resolve font-size from external/linked styles

Changes: https://git.openjdk.org/jdk/pull/10054/files
 Webrev: https://webrevs.openjdk.org/?repo=jdk&pr=10054&range=00
  Issue: https://bugs.openjdk.org/browse/JDK-8292948
  Stats: 10 lines in 1 file changed: 5 ins; 4 del; 1 mod
  Patch: https://git.openjdk.org/jdk/pull/10054.diff
  Fetch: git fetch https://git.openjdk.org/jdk pull/10054/head:pull/10054

PR: https://git.openjdk.org/jdk/pull/10054