Use black for font outlines by default instead of white

[Calinou]

This makes font outlines more usable out of the box, as black is one of the most commonly used colors for font outlines.

Now, to configure a working font outline, you just have to increase Outline Size in a supported Control node's custom constants:

[KoBeWi]

White outlines are actually useful when combined with outline modulate. Question is whether black is more common that all other colors 🤔

[Calinou]

White outlines are actually useful when combined with outline modulate. Question is whether black is more common that all other colors thinking

Should we make outline modulate black by default instead (and keep the outline glyphs white)?

[YuriSizov]

Should we make outline modulate black by default instead (and keep the outline glyphs white)?

Let's do that!

[YuriSizov]

I think this is something we can change in 4.x now.

[Mickeon]

A whole year has passed and it seems like this was extremely desirable back when. How do we feel about this now?

[Calinou]

Rebased and tested again, it works as expected.

Should we make outline modulate black by default instead (and keep the outline glyphs white)?

I don't remember what this was about though. outline_modulate is only referenced in Window and Label3D (the latter is already solid black by default).

[KoBeWi]

outline_modulate was a theme color. It was used to modulate the outline color defined in Font (which this PR modified originally I think?), but the Font outline is now gone.

[akien-mga]

There are some style issues, clang-format didn't run.

[akien-mga]

Seems fine to me after fixing style issues.

[akien-mga]

Thanks!