RFR: 8372103: Metal JButton doesn't show focus if no text or icon

[Prasanta Sadhukhan]

If a JButton in Metal Look&Feel has no text or icon, it will not show an indicator when selected.
Fix is made to show a focus rectangle even for empty button

Before fix
<img width="347" height="300" alt="image" src="https://github.com/user-attachments/assets/d03c64b2-8570-4585-a3a9-732a9c98d880" />

After fix
<img width="350" height="365" alt="image" src="https://github.com/user-attachments/assets/98b4e6c2-1976-4f83-bff3-5ff30a6e04d8" />

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Commit messages:
 - jcheck
 - 8372103: Metal JButton doesn't show focus if no text or icon

Changes: https://git.openjdk.org/jdk/pull/28408/files
  Webrev: https://webrevs.openjdk.org/?repo=jdk&pr=28408&range=00
  Issue: https://bugs.openjdk.org/browse/JDK-8372103
  Stats: 82 lines in 2 files changed: 81 ins; 0 del; 1 mod
  Patch: https://git.openjdk.org/jdk/pull/28408.diff
  Fetch: git fetch https://git.openjdk.org/jdk.git pull/28408/head:pull/28408

PR: https://git.openjdk.org/jdk/pull/28408