Replace color prop of LoadingIcon with style prop

[raimund-schluessler]

How about a prop style (or similar name) with the options dark, light and auto (being default).

Yes, perfect!

@jancborchardt for 4, this what we're discussing.
You need to be able to force light or dark. See previous comments.

another one which works on the primary color (e.g. in header or buttons), depending on server theming
possibly another one in primary color which works in these new buttons we use some places which are color-primary-light. (Worst case we just use 1) for those too.)

We do not use the loading primary anywhere at nextcloud. Please provide clear guidelines on why and when to use them in an issue so we can implement this if it's really necessary 🙏

Originally posted by @skjnldsv in #2727 (comment)