Apply VectorDrawable density scaling before applying theme

Refactors density handling to look more similar to GradientDrawable's
implementation, which should make things easier to maintain. We no
longer update density directly in updateStateFromTypedArray, instead
handling it in applyTheme() and inflate().

Lazily calculates local density-dependent dimensions and invalidates
when the constant state density changes, which should ensure a random
call to applyTheme() will still result in the correct intrinsic
dimensions.

Change-Id: I726878a6cd75d38a550637e3e7a7b6bc68bcaf6d