RFR: 8374909: CodeArea: Exception in IME [v3]

[Andy Goryachev]

> Fixes a bug which was reported in https://github.com/andy-goryachev-oracle/Test/issues/6#issuecomment-3726867016 (introduced by adding IME support https://bugs.openjdk.org/browse/JDK-8368478 )
> 
> Adds proper clamping and normalization of selection range within the `StyledTextModel`, and replaces the implementation of getText() with the standard export().

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

 - Merge branch 'master' into 8374909.exception
 - limit
 - lf
 - whitespace
 - fix
 - tests

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Changes: https://git.openjdk.org/jfx/pull/2029/files
  Webrev: https://webrevs.openjdk.org/?repo=jfx&pr=2029&range=02
  Stats: 328 lines in 8 files changed: 280 ins; 31 del; 17 mod
  Patch: https://git.openjdk.org/jfx/pull/2029.diff
  Fetch: git fetch https://git.openjdk.org/jfx.git pull/2029/head:pull/2029

PR: https://git.openjdk.org/jfx/pull/2029