Add a setting to control selection foreground color

This is highly related to #3326/#3471 and #3561.

We've added a setting to control what color we use to highlight text with when it's selected in #3471.

However, that doesn't necessarily fix our contrast ratio problems w.r.t. selection, since the configured color might still not have enough difference from the foreground of the highlighted text.

Conhost had an inverting selection, which didn't have this problem. However, we think that might be Hard to implement in the dx renderer. Adding that to the Terminal is being tracked in #3561.

A selection foreground color A: might be more feasible to implement B: is a good configurable setting to add regardless, to enable further personalization of the terminal.

Implementation might still be tricky though, since the Renderer is only ever told about the selection rects after it has drawn the text. Re-drawing the text seems like a bad idea. I'm not sure we'll be able to re-order things in the Renderer safely without also impacting the GDI and other rendering heads. This is hard, but easier than inverting selection.