RFR: 8370140: RichTextArea: line endings [v18]

[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), with convenience setter and getter in the `RichTextArea`.
> 
> ### NOTES
> 
> - some dependency on #1938 , resolved.

Andy Goryachev has updated the pull request incrementally with one additional commit since the last revision:

  system

-------------

Changes:
  - all: https://git.openjdk.org/jfx/pull/1944/files
  - new: https://git.openjdk.org/jfx/pull/1944/files/576a8575..e6a2c842

Webrevs:
 - full: https://webrevs.openjdk.org/?repo=jfx&pr=1944&range=17
 - incr: https://webrevs.openjdk.org/?repo=jfx&pr=1944&range=16-17

  Stats: 3 lines in 1 file changed: 0 ins; 0 del; 3 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