fix writing composable impl for generic default interfaces

[stevenbrix]

for composable classes with generic default interfaces, we were incorrectly writing type names like IVector<Foo>, which aren't valid swift type names. This uses the same bind_type_abi method we use for removing the brackets and writing a name like IVectorFoo instead.

This error didn't manifest itself until trying to use the ThemeShadow class which resulted in UIWeakElementCollection being generated, which is unsealed.

Changes

1. description above
2. Had to change typealias SwiftABI = IVectorFoo to the full name since there is a naming collision now
3. updated one of the class definitions to be unsealed to verify the fix works

Fixes WIN-1015