Deprecate theme-color, gray, color functions

[MartijnCuppens]

As suggested here #27338 (comment), we can deprecate the theme-color, gray, color functions. The color and gray functions are not used by Bootstrap and it's easy to remove the theme-color dependency. These functions don't really add anything to Bootstrap.

With a small changes we can make Bootstrap independent of these functions and throw a warning like we did here, so we can deprecate them in a next major release:

bootstrap/scss/mixins/_text-hide.scss

Lines 10 to 12 in f59c2d9

	@if ($ignore-warning != true) {
	@warn "The `text-hide()` mixin has been deprecated as of v4.1.0. It will be removed entirely in v5.";
	}

[XhmikosR]

Personally I'd say go for this, but perhaps wait for @mdo and @andresgalante to chime in.

We just need to make sure we don't introduce breaking changes in minor/patch releases.

[mdo]

I think the expectation I had here was that functions like theme-color would generate the different shades of each color, allowing us to easily create a family of one color's shades (e.g., our $gray-100 through $gray-900). I imagine we can nuke these in v5 if we're not using them though.

[mdo]

I believe this was resolved.