Build step to inline CSS imports

[James Burke]

Have the build inline CSS imports.

It will need to account for path changes in the styles.

[James Burke]

(In [12248]) Fixes #5646. Inlining CSS imports with url() path conversions. Additional whitespace removal too. !strict

[James Burke]

Reading the spec some more, we should add support for:

@import "file.css";

and we should probably not inline rules that have a media designation:

@import url("bluish.css") projection, tv;

except, when the media designation is "all".

[James Burke]

(In [12292]) Fixes #5646. Allow import calls without url() and ignore import calls that have media types other than 'all'. !strict