gc2stack: Extract static size checking code into helper function.
gc2stack: Move TypeInfo handling code into FunctionInfo subclass.

This is to properly support calls that don't involve TypeInfo
at all, like it is already the case for _d_newclass, and will be
for _d_allocmemory.
gc2stack: Handle _d_allocmemory.

This allows us to clean up after inlining closures.