Add default-features=false

[wakewakame]

Hi, thank you for creating and maintaining this library.

While developing a VST plugin with nih-plug, I noticed that epaint_default_fonts—which has a GPL-incompatible license—is pulled in via nih-plug-egui, even when I try to disable default-features:

-nih_plug_egui = { git = "...", rev = "..." }
+nih_plug_egui = { git = "...", rev = "...", default-features = false, features = ["opengl"] }

It seems egui-baseview is included with default-features enabled by default. This PR disables them, so users can opt into only the features they need.

[robbert-vdh]

Disabling default features for some of these things is probably not a bad thing! Which of epaint_default_fonts is not GPL compatible though? It at last claims to be licensed under your pick of MIT or Apache 2.0 for the code, and the fonts are licensed under the OFL 1.1 and the Ubuntu Fonts license 1.0.

[wakewakame]

Thank you for reviewing this PR.

I'm not very familiar with license details, so I initially thought there was a compatibility issue because OFL 1.1 is listed as GPL-incompatible. After submitting the PR, I realized that embedding an OFL font in a GPL application is generally acceptable. Sorry for the confusion, and thank you for pointing it out.

That said, adding default-features = false should have no negative impact on users, and it allows those who don't need the font to avoid the extra dependency. I would be happy if this could still be merged for that reason.