RFR: JDK-8282772: JButton text set as HTML content has unwanted padding [v4]

[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.

DamonGuy has updated the pull request incrementally with one additional commit since the last revision:

  Added string buffer. Separated fail images. Changed exception to throw at the end of test.

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Changes:
  - all: https://git.openjdk.java.net/jdk/pull/8407/files
  - new: https://git.openjdk.java.net/jdk/pull/8407/files/cc5091fa..82d9ca27

Webrevs:
 - full: https://webrevs.openjdk.java.net/?repo=jdk&pr=8407&range=03
 - incr: https://webrevs.openjdk.java.net/?repo=jdk&pr=8407&range=02-03

  Stats: 18 lines in 1 file changed: 15 ins; 0 del; 3 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