Adds the ability to manually handle the terminal renderer resizing
events by allowing different render size and WPF control size. This is
done by adding an `AutoFill` property to the control that prevents the
renderer from automatically resizing and tells the WPF control to fill
in the extra space with the terminal background as shown below:
This PR adds the following:
- Helper method in the DX engine to convert character viewports into
pixel viewports
- `AutoFill` property that prevents automatic resizing of the renderer
- Tweaks and fixes that automatically fill in the empty space if
`AutoFill` is set to false
- Fixes resizing methods and streamlines their codepath
## Validation Steps Performed
Manual validation with the Visual Studio Integrated Terminal tool
window.
9e86e29584