[jfx17u] RFR: 8087557: [Win] [Accessibility, Dialogs] Alert Dialog content is not fully read by Screen Reader

[Ambarish Rapte]

Backport this a11y fix to jfx17u.
This is not a clean backport. The source code changes apply cleanly but there was a conflict in test file.
The test `DialogTest.java` file does not exist in jfx17u source.
The file is now added but only with one test that was added as part of this fix to mainline, and other pre-existing tests are removed.
Tested that fix works as expected on Windows and macOS

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Commit messages:
 - remove unused import
 - 8087557: [Win] [Accessibility, Dialogs] Alert Dialog content is not fully read by Screen Reader

Changes: https://git.openjdk.org/jfx17u/pull/91/files
 Webrev: https://webrevs.openjdk.org/?repo=jfx17u&pr=91&range=00
  Issue: https://bugs.openjdk.org/browse/JDK-8087557
  Stats: 89 lines in 6 files changed: 88 ins; 0 del; 1 mod
  Patch: https://git.openjdk.org/jfx17u/pull/91.diff
  Fetch: git fetch https://git.openjdk.org/jfx17u pull/91/head:pull/91

PR: https://git.openjdk.org/jfx17u/pull/91