8356042: RichTextArea: tab stops attributes

[andy-goryachev-oracle]

• adds tab stops paragraph attributes to the RichTextArea
• adds a ruler to the RichEditorDemoApp example

NOTE:
This PR requires changes in #1813 (JDK-8357393) to be integrated first.

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Progress

• Change must be properly reviewed (1 review required, with at least 1 Reviewer)
• Change must not contain extraneous whitespace
• Commit message must refer to an issue

Issue

• JDK-8356042: RichTextArea: tab stops attributes (Enhancement - P4)

Reviewing

Using git

Checkout this PR locally:
$ git fetch https://git.openjdk.org/jfx.git pull/1800/head:pull/1800
$ git checkout pull/1800

Update a local copy of the PR:
$ git checkout pull/1800
$ git pull https://git.openjdk.org/jfx.git pull/1800/head

Using Skara CLI tools

Checkout this PR locally:
$ git pr checkout 1800

View PR using the GUI difftool:
$ git pr show -t 1800

Using diff file

Download this PR as a diff file:
https://git.openjdk.org/jfx/pull/1800.diff

[openjdk]

⚠️ @andy-goryachev-oracle This pull request contains merges that bring in commits not present in the target repository. Since this is not a "merge style" pull request, these changes will be squashed when this pull request in integrated. If this is your intention, then please ignore this message. If you want to preserve the commit structure, you must change the title of this pull request to Merge <project>:<branch> where <project> is the name of another project in the OpenJDK organization (for example Merge jdk:master).