Redesigns the volume panel, take 2!

Now that ag/13665338 is in, we shouldn't see crashes related to the AlphaTintDrawableWrapper anymore, so we can try this again.

This is nearly identical to ag/13535305, with two changes:
1) we pass the Theme to getDrawable() so we don't see warnings in logcat about undefined theme attributes
2) we use a placeholder drawable in the XML drawables instead of @android:color/transparent, which caused issues with the first tint not being applied

Bug: 171441100
Test: atest SystemUITests
Test: manual
Change-Id: I91c6e6430bb15e4f921aa0bd45f505c26db5aca4