RFR: 8258970: Disabled JPasswordField foreground color is wrong with GTK LAF

[Abhishek Kumar]

Disabled JPasswordField foreground color was not grayed out in GTK LAF.

The foreground color in disabled state was close to black color (RGB 0,0,0) for password field which is not differentiable from enabled state foreground color.

To fix for this problem, the widget type is changed to `TEXT_AREA `for disable password field which returns the foreground color as gray. Checked with Oracle linux as well and fix worked fine.

An automated test case has been added and checked in CI, link is added in JBS. Test mentioned in JBS also works fine with the fix.

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Commit messages:
 - JPasswordField disabled foreground color fix

Changes: https://git.openjdk.org/jdk/pull/15263/files
 Webrev: https://webrevs.openjdk.org/?repo=jdk&pr=15263&range=00
  Issue: https://bugs.openjdk.org/browse/JDK-8258970
  Stats: 130 lines in 2 files changed: 130 ins; 0 del; 0 mod
  Patch: https://git.openjdk.org/jdk/pull/15263.diff
  Fetch: git fetch https://git.openjdk.org/jdk.git pull/15263/head:pull/15263

PR: https://git.openjdk.org/jdk/pull/15263