RFR: 7124282: [macosx] Can't see table cell highlighter when the highlight border is the same color as the cell. [v6]

[Harshitha Onkar]

> Previously while tabbing through the JTable cell, the cell highlighter/focus ring was not visible against the selection background. 
> 
> Changes are made to Aqua LAF to derive a lighter focus ring color by changing saturation and setting brightness component to 100% of selection background color so that it is visible while tabbing through `JTable` cells. A new method is added for this purpose which takes in `selectionBackground` color, does adjustment to saturation and brightness manipulation and returns a new focus ring color. There are edge cases where the HSB transformation does not yield the right focus ring color, for these cases a default color is returned that can be seen against the `selectionBackground`.
> 
> **Edge Cases**
> **Selection Background**     -----       **Returned Focus Ring Color**
> - White/ Black/Gray                        ----->          Light Gray
> 
> The following HSB chart was used [Chart Link](https://codepen.io/HunorMarton/details/eWvewo), to determine the best saturation offsets used in deriveContrastFocusRing method.
> 
> A test case is added to compare the RGB difference between the original focus ring color & selection background and the brighter focus ring color & selection background.
> 
> PS: The native L&F (Mac OS) and Swing L&F for JTable cell tabbing differs (on native tables the cell background turns white on focus with a cell focus ring). Since the background for Swing tables can be set by users and also overridden by subclassing `DefaultTableCellRenderer`, and to adhere to current implementation of Swing, the white cell background changes are not incorporated. Only the Focus Ring/ Cell Highlighter is made more prominent against the selection background.

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

  on-the-fly focus ring color changes added

-------------

Changes:
  - all: https://git.openjdk.java.net/jdk/pull/7768/files
  - new: https://git.openjdk.java.net/jdk/pull/7768/files/c71358dd..f6c9b6c0

Webrevs:
 - full: https://webrevs.openjdk.java.net/?repo=jdk&pr=7768&range=05
 - incr: https://webrevs.openjdk.java.net/?repo=jdk&pr=7768&range=04-05

  Stats: 61 lines in 3 files changed: 31 ins; 1 del; 29 mod
  Patch: https://git.openjdk.java.net/jdk/pull/7768.diff
  Fetch: git fetch https://git.openjdk.java.net/jdk pull/7768/head:pull/7768

PR: https://git.openjdk.java.net/jdk/pull/7768