Closes#33253 in a way that doesn't regress #32175 - namely,
automatically adjusts the contrast between the foreground and background
text in the terminal such that it's above a certain threshold. The
threshold is configurable in settings, and can be set to 0 to turn off
this feature and use exactly the colors the theme specifies even if they
are illegible.
## One Light Theme Before
<img width="220" alt="Screenshot 2025-07-07 at 6 00 47 PM"
src="https://github.com/user-attachments/assets/096754a6-f79f-4fea-a86e-cb7b8ff45d60"
/>
(Last row is highlighted because otherwise the text is unreadable; the
foreground and background are the same color.)
## One Light Theme After
(This is with the new default contrast adjustment setting.)
<img width="215" alt="Screenshot 2025-07-07 at 6 22 02 PM"
src="https://github.com/user-attachments/assets/b082fefe-76f5-4231-b704-ff387983a3cb"
/>
This approach was inspired by @mitchellh's use of automatic contrast
adjustment in [Ghostty](https://ghostty.org/) - thanks, Mitchell! The
main difference is that we're using APCA's formula instead of WCAG for
[these
reasons](https://khan-tw.medium.com/wcag2-are-you-still-using-it-ui-contrast-visibility-standard-readability-contrast-f34eb73e89ee).
Release Notes:
- Added automatic dynamic contrast adjustment for terminal foreground
and background colors
Richard Feldman
9b7632d5f6