Introduce `ensureTypedArrayCapacity` typed array utility function and use it in ShapeData

Will be used in other places, too, in a bit.
Activate parsing of morph shapes again

... in a heavily modified form, though: morph end coordinates are now stored in their own buffer, and a `MorphShapeSymbol` is introduced for dealing with those coordinates and the fill and line bounds.
Cleanup
Store morph shape metadata in MorphShape instances
Merge pull request #1380 from tschneidereit/nat

Morphs 0: The Prequel