RFR: 8092102: Labeled: truncated property

[Andy Goryachev]

Adds Labeled.truncated property which indicates when the text is visually truncated (and the ellipsis string is inserted) in order to fit the available width.

The new property reacts to changes in the following properties:
- ellipsisString
- font
- text
- width
- wrapText

For some reason, line 859 generates a javadoc "co comment" warning, despite the javadoc comment present at the property declaration in line 832.

I don't think it's worth creating a headful test (headless won't work) due to relative simplicity of the code.

**Alternative**

The desired functionality can be just as easily achieved on an application level, by adding a similar property to a subclass.  What is the benefit of adding this functionality to the core?

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Commit messages:
 - 8092102 Labeled: truncated property

Changes: https://git.openjdk.org/jfx/pull/1389/files
 Webrev: https://webrevs.openjdk.org/?repo=jfx&pr=1389&range=00
  Issue: https://bugs.openjdk.org/browse/JDK-8092102
  Stats: 80 lines in 1 file changed: 59 ins; 17 del; 4 mod
  Patch: https://git.openjdk.org/jfx/pull/1389.diff
  Fetch: git fetch https://git.openjdk.org/jfx.git pull/1389/head:pull/1389

PR: https://git.openjdk.org/jfx/pull/1389