RFR: 8370140: RichTextArea: line endings [v7]

[Andy Goryachev]

> Adds control of line endings (newline separators) in `StyledTextModel`, `RichTextArea`, and `CodeArea`.
> 
> The impacted areas are:
> - saving to plain text
> - copying to plain text
> - IME
> 
> This feature is implemented as a regular field in the `StyledTextModel` (since it is ultimately an attribute of the model), and as a property in the `CodeArea`.
> 
> NOTE:
> - some dependency on #1938 , resolved.

Andy Goryachev has updated the pull request with a new target base due to a merge or a rebase. The pull request now contains nine commits:

 - non-nullable
 - Merge branch 'master' into 8370140.line.separator
 - get text
 - Merge branch 'master' into 8370140.line.separator
 - since
 - Merge branch 'master' into 8370140.line.separator
 - Merge remote-tracking branch 'origin/master' into 8370140.line.separator
 - tests
 - line endings

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Changes: https://git.openjdk.org/jfx/pull/1944/files
  Webrev: https://webrevs.openjdk.org/?repo=jfx&pr=1944&range=06
  Stats: 270 lines in 13 files changed: 239 ins; 11 del; 20 mod
  Patch: https://git.openjdk.org/jfx/pull/1944.diff
  Fetch: git fetch https://git.openjdk.org/jfx.git pull/1944/head:pull/1944

PR: https://git.openjdk.org/jfx/pull/1944