[jfx15] RFR: 8176270: Adding ChangeListener to TextField.selectedTextProperty causes StringOutOfBoundsException [v8]

[Robert Lichtenberger]

> This PR fixes JDK-8176270 by clamping the end index of the selected text to the length of the text.

Robert Lichtenberger has updated the pull request incrementally with one additional commit since the last revision:

  8176270: Adding ChangeListener to TextField.selectedTextProperty causes StringOutOfBoundsException
  
  Fix check condition in RTest.
  Replace underscore based variable names.

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Changes:
  - all: https://git.openjdk.java.net/jfx/pull/138/files
  - new: https://git.openjdk.java.net/jfx/pull/138/files/bf9e08d7..3dd80c78

Webrevs:
 - full: https://webrevs.openjdk.java.net/jfx/138/webrev.07
 - incr: https://webrevs.openjdk.java.net/jfx/138/webrev.06-07

  Stats: 6 lines in 2 files changed: 0 ins; 0 del; 6 mod
  Patch: https://git.openjdk.java.net/jfx/pull/138.diff
  Fetch: git fetch https://git.openjdk.java.net/jfx pull/138/head:pull/138

PR: https://git.openjdk.java.net/jfx/pull/138