Correct Default Application Selector styles for high contrast and to change with OS theme dark/light toggle
## References
- https://docs.microsoft.com/windows/uwp/design/controls-and-patterns/xaml-theme-resources
## PR Checklist
* [x] Closes#10181
* [x] I work here
* [x] Manual tests passed
## Detailed Description of the Pull Request / Additional comments
1. If I'm going to override colors, I need to define styles in a resource dictionary with Light, Dark, and HighContrast variants so it can be appropriate for each of those.
2. For HighContrast, I need to not mess with text colors and let them follow the default settings.
3. For using System Brushes, I need to use a `ThemeResource` binding not a `StaticResource` binding. The former lets it change when you flip the OS toggle Light/Dark. The latter is stuck to whatever it was when the page loaded.
## Validation Steps Performed
- Loaded in light mode. Flipped to dark. Watched it change live. Checked both unselected and rollover/selected to ensure it was fine.
- Loaded in dark mode. Flipped to light. Watched it change live. Checked both unselected and rollover/selected to ensure it was fine.
- Flipped to HC. Watched it change live. Confirmed that unselected is black/white contrast and the roll over has the cyan/black. (No longer uses special second-line brush for HC, matches the controls I modeled this one on from OS Settings).
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