RFR: 8299522: Incorrect size of Approve button in custom JFileChooser [v13]

[Tejesh R]

> FileChooser Open/Approve button size is shown incorrectly when no Approve button text is set in `CUSTOM_DIALOG` type. Reason being that no default Approve Button text is returned during Dialog Type Property change. Since `null` is returned as Button string the Button size is incorrectly shown. The fix here addresses the issue by adding a default Approve Button Text when no text is set explicitly in case of `CUSTOM_DIALOG` type.
> Automated test is attached which has been tested with multiple test runs.

Tejesh R has updated the pull request with a new target base due to a merge or a rebase. The incremental webrev excludes the unrelated changes brought in by the merge/rebase. The pull request contains 14 additional commits since the last revision:

 - Copyright update
 - Merge branch 'master' of https://git.openjdk.java.net/jdk into branch_8299522
 - Remove unused imports
 - Tooltip and Mnemonic checks added to test
 - Updated JTREG summary
 - Added Aqua L&F -  linked to #12008 fix
 - Updated based on review comments
 - Updated based on review comments
 - Updated based on review comments
 - Spacing updation
 - ... and 4 more: https://git.openjdk.org/jdk/compare/08eddab8...0ca14f69

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Changes:
  - all: https://git.openjdk.org/jdk/pull/11901/files
  - new: https://git.openjdk.org/jdk/pull/11901/files/8c3d5c00..0ca14f69

Webrevs:
 - full: https://webrevs.openjdk.org/?repo=jdk&pr=11901&range=12
 - incr: https://webrevs.openjdk.org/?repo=jdk&pr=11901&range=11-12

  Stats: 125478 lines in 4204 files changed: 54798 ins; 29112 del; 41568 mod
  Patch: https://git.openjdk.org/jdk/pull/11901.diff
  Fetch: git fetch https://git.openjdk.org/jdk pull/11901/head:pull/11901

PR: https://git.openjdk.org/jdk/pull/11901