## Summary of the Pull Request

When we're on acrylic, we can't have cleartype text unfortunately. This PR changes the DX renderer to force cleartype runs of text that are on a non-opaque background to use grayscale AA instead.

## References

Here are some of the URLS I was referencing as writing this:

* https://stackoverflow.com/q/23587787
* https://docs.microsoft.com/en-us/windows/win32/direct2d/supported-pixel-formats-and-alpha-modes#cleartype-and-alpha-modes
* https://devblogs.microsoft.com/oldnewthing/20150129-00/?p=44803
* https://docs.microsoft.com/en-us/windows/win32/api/d2d1/ne-d2d1-d2d1_layer_options
* https://docs.microsoft.com/en-us/windows/win32/direct2d/direct2d-layers-overview#d2d1_layer_parameters1-and-d2d1_layer_options1
* https://docs.microsoft.com/en-us/windows/win32/api/dcommon/ne-dcommon-d2d1_alpha_mode?redirectedfrom=MSDN#cleartype-and-alpha-modes
* https://stackoverflow.com/a/26523006

Additionally:
* This was introduced in #4711 

## PR Checklist
* [x] Closes #5098
* [x] I work here
* [ ] Tests added/passed
* [n/a] Requires documentation to be updated

## Detailed Description of the Pull Request / Additional comments

Basically, if you use cleartype on a light background, what you'll get today is the text foreground color _added_ to the background. This will make the text look basically invisible. 

So, what I did was use some trickery with `PushLayer` to basically create a layer where the text would be forced to render in grayscale AA. I only enable this layer pushing business when both:
  * The user has enabled cleartype text
  * The background opacity < 1.0

This plumbs some information through from the TermControl to the DX Renderer to make this smooth.

## Validation Steps Performed

Opened both cleartype and grayscale panes SxS, and messed with the opacity liberally.