[eclipse-pmc] API Addition: Preference Constants For Hover Colors

[Daniel Megert <daniel_megert@xxxxxxxxxx>]

In order to provide let users configure the hover background and foreground
color I need to add two new preference constants:
- AbstractTextEditor.PREFERENCE_COLOR_HOVER_FOREGROUND
- AbstractTextEditor.PREFERENCE_COLOR_HOVER_FOREGROUND_SYSTEM_DEFAULT
- AbstractTextEditor.PREFERENCE_COLOR_HOVER_BACKGROUND
- AbstractTextEditor.PREFERENCE_COLOR_HOVER_BACKGROUND_SYSTEM_DEFAULT


GOALS/BENEFITS:
- allow to user to configure the hover background and foreground color
- fix a long outstanding bug with many votes


CORRESPONDING BUG:
- [preferences] Tooltip and info views background color clashes with editor
colors
      https://bugs.eclipse.org/bugs/show_bug.cgi?id=41867


RISKS:
No risks as the default will be the current colors.


PERFORMANCE IMPACTS:
None.


Dani