This is a first step in reversing the dependency flow around the `theme`
package in MDC. In a future commit, I'll make theme contain all the various
MaterialComponents theme definitions, and it will thus depend on the various
packages containing our components (widget, button, toggle, etc.).
The theme package will be empty as of this commit, but since I plan to use it
in the next one I've left the build infrastructure in place.
PiperOrigin-RevId: 180737806
Bazel is happier if Java/Java test roots are named 'java' and 'javatests', and
this will mean that once we create a BUILD file for
android/support/design/{widget,internal}/ we'll no longer need a custom package
specified in our build (which tends to cause build problems that manifest quite
weirdly). This commit doesn't attempt to refactor the build at all yet, and is
just a pure move.
PiperOrigin-RevId: 178060739
