RFR: 8318101: Additional test cases for CSSAttributeEqualityBug

[Alexey Ivanov]

Adds additional test cases to `javax/swing/text/html/CSS/CSSAttributeEqualityBug.java`.

Currently, CSS parser in Java allows space between the number and the unit or percent. This is what the additional test cases verify.

There's also one additional case for `border-width: medium`.

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Commit messages:
 - 8318101: Additional test cases for CSSAttributeEqualityBug

Changes: https://git.openjdk.org/jdk/pull/16193/files
 Webrev: https://webrevs.openjdk.org/?repo=jdk&pr=16193&range=00
  Issue: https://bugs.openjdk.org/browse/JDK-8318101
  Stats: 25 lines in 1 file changed: 23 ins; 1 del; 1 mod
  Patch: https://git.openjdk.org/jdk/pull/16193.diff
  Fetch: git fetch https://git.openjdk.org/jdk.git pull/16193/head:pull/16193

PR: https://git.openjdk.org/jdk/pull/16193