Previously [most of] the components were either in `widget` or depended on it,
and all theme-related resources (attributes, styles, etc.) were placed there.
This structure doesn't really work for our goals, and makes it harder to split
components by functional area. In this commit, I move all the theme definitions
to `theme` (as well as `dialog` and `bottomsheet` since they also have relevant
themes, and splitting them into separate packages is the only way to make the
dep tree non-circular). Component packages declare their own theme attributes
(e.g. `chip` declares all the theme attributes necessary for chips), as well as
styles, colors, dimens, drawables, etc.
This move isn't entirely complete in this commit, but it is enough to get
things building with this setup. I'll move the rest of the components' resources
in follow-up commits.
PiperOrigin-RevId: 182611275
