RFR: JDK-8282772: JButton text set as HTML content has unwanted padding

[DamonGuy]

The insets for buttons were incorrect for L&Fs except for Aqua when the text is set to HTML. This was fixed in Aqua by adding a conditional to check for the BasicHTML property key in the button component. This same logic can be used to fix Metal & Motif L&Fs in BasicButtonUI, but Nimbus is not fixed by this. Nimbus gets its default values from a skin.laf file, and when the defaults here are set to have left & right insets to 0 for ButtonUI, the issue is fixed. I also tested for non-HTML text after the changes, and the changes do not affect normal text.

The HtmlButtonImageTest has been changed to cycle through all L&Fs available on a device.

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Commit messages:
 - Added conditional for HTML in BasicButtonUI. Edited default Nimbus ButtonUI insets. Edited HtmlButtonImageTest to cycle all L&Fs. Recreated this branch to fix sync issue.

Changes: https://git.openjdk.java.net/jdk/pull/8407/files
 Webrev: https://webrevs.openjdk.java.net/?repo=jdk&pr=8407&range=00
  Issue: https://bugs.openjdk.java.net/browse/JDK-8282772
  Stats: 67 lines in 3 files changed: 45 ins; 4 del; 18 mod
  Patch: https://git.openjdk.java.net/jdk/pull/8407.diff
  Fetch: git fetch https://git.openjdk.java.net/jdk pull/8407/head:pull/8407

PR: https://git.openjdk.java.net/jdk/pull/8407