RFR: 8360070: AccessibleText.getBeforeIndex returns null for last character [v3]

[Abhishek Kumar]

> `AccessibleText.getBeforeIndex` method returns `null for last characte`r due to the **wrong boundary value condition check**.
> This method returns `null` when the `passed index parameter` is equal to `text's length` which is incorrect.
> `getBeforeIndex` method should return `null` only if the **passed index parameter is less than 0 and greater than the text's length**.
> 
> After modifying the condition check, expected character is returned. Test is added to verify the check,

Abhishek Kumar has updated the pull request incrementally with one additional commit since the last revision:

  Test extended for WORD and SENTENCE

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Changes:
  - all: https://git.openjdk.org/jdk/pull/25941/files
  - new: https://git.openjdk.org/jdk/pull/25941/files/b7852974..e9c5ae37

Webrevs:
 - full: https://webrevs.openjdk.org/?repo=jdk&pr=25941&range=02
 - incr: https://webrevs.openjdk.org/?repo=jdk&pr=25941&range=01-02

  Stats: 21 lines in 1 file changed: 14 ins; 1 del; 6 mod
  Patch: https://git.openjdk.org/jdk/pull/25941.diff
  Fetch: git fetch https://git.openjdk.org/jdk.git pull/25941/head:pull/25941

PR: https://git.openjdk.org/jdk/pull/25941