InlineHints are unreadable in Windows High Contrast mode

[JoeRobich]

Version Used: VS 17.8p1

Steps to Reproduce:

1. Go to Windows settings
2. Enable a Contrast Theme (Night Sky for instance)
3. Open VS with InlineHints enabled

Need to add entries in the VS2017 and VS2019 color scheme xml files for the HighContrast theme otherwise they fall back to the colors set in their FormatDefinition. InlineHint's background is near white and the Type's foreground color is also near white.

FYI @akhera99

[CyrusNajmabadi]

@akhera99 Is this still the case? Is this an accessibility tenet we need to fix?