The only difference between clip-path and shape-outside is the reference box
enum, so I generalize StyleClipPath to be a template struct StyleShapeSource to
accommodate both. I'll have to move all the method definition to the header to
make the linker happy.
The only logic change is calling operator==() instead of EqualURIs to compare
urls in StyleShapeSource::operator==().
MozReview-Commit-ID: LOBGVVpnnB
Rename StyleBasicShape to StyleBasicShapeType in nsStyleConsts.h, and
replace the old enum nsStyleBasicShape::Type by the enum class
StyleBasicShapeType.
Also, replace NS_ASSERTION() by MOZ_ASSERT().
MozReview-Commit-ID: EuS4ZtYKsk6
