12219 adjust widget header contrast

[arthanson]

Fixes: #12219

1. updates foreground_color template tag to work with color values "red" instead of hex values.
2. change widget template to use this for text and icons
3. adds some utility functions to lighten (and darken) a color, used to make gear and close icons lighter then text

[arthanson]

@jeremystretch went through all the colors in dark mode and it works there as well. However "Default" on dark mode doesn't work (black on dark-grey) however IMHO we should look at a separate issue/bug to remove or replace Default as it currently uses outline-dark which is not a color and is just he widget background color which is not very useful in either dark or light mode. I don't think it is possible to fix this for Default as it is the background widget color that changes between dark and light mode which isn't detectable from python. I think removing default should be a separate issue as it will require some migrations and we may want to refactor widget color more.

This fixes the text color for widgets and I think is useful, it just doesn't fix it for dark mode default (which should probably be removed).

[github-actions]

This PR has been automatically marked as stale because it has not had recent activity. It will be closed automatically if no further action is taken.

[jeremystretch]

I'm to close this out in favor of the simpler fix in PR #13753. We may reconsider something more elegant as part of the upcoming UI refresh.