<Swing Dev> RFR: 8256019: JLabel HTML text does not support translucent text colors

[Prasanta Sadhukhan]

Issue is a JLabel with a translucent foreground color properly renders plain text, but with HTML text, the alpha component is discarded and the text is rendered using an opaque color.
As per https://www.w3schools.com/cssref/func_rgba.asp, CSS supports rgba() to support alpha and render translucent text color
but support for rgba() is not present in JDK html text rendering.

Added support for rgba() to render translucent text color.

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Commit messages:
 - Initial fix

Changes: https://git.openjdk.java.net/jdk/pull/1158/files
 Webrev: https://webrevs.openjdk.java.net/?repo=jdk&pr=1158&range=00
  Issue: https://bugs.openjdk.java.net/browse/JDK-8256019
  Stats: 251 lines in 5 files changed: 224 ins; 2 del; 25 mod
  Patch: https://git.openjdk.java.net/jdk/pull/1158.diff
  Fetch: git fetch https://git.openjdk.java.net/jdk pull/1158/head:pull/1158

PR: https://git.openjdk.java.net/jdk/pull/1158