[FEATURE] Make the retro terminal mode more configurable

[spudpiggy]

Description of the new feature/enhancement

Retro terminal mode looks cool, but it also makes text really hard to see on my secondary (which is a crappy old Dell) and doesn't do much of anything on my primary (a 1080p tv, idk size in inches) I'd like if it were more configurable, so that I could tweak it to be more/less effective.

Proposed technical implementation details (optional)

Allow the following to be changed:

• Width of scanlines
• Size of the gap between two scanlines
• How dark that gap is
• How much glow is added to text; 0% is none, 100% is current, and 200% is 2x the current amount.

These settings should be applied on a per-monitor basis, since different monitors will need different amounts of tweaking.

[zadjii-msft]

Good news! The retro shader is just a specific example of custom pixel shaders for the Terminal. You can feel free to grab the source from Retro.hlsl, and modify it however you'd like!