Reorder _validate_parameter_type to avoid isclass check

[michaeldiamant]

Reorders checks in Reorder _validate_parameter_type to avoid isclass check.

Rationale: Since there was some discussion on the topic in #256 (comment), I paired with @tzaffi to better understand the runtime type system checks. While pairing, we observed that it's possible to remove a check and retain equivalent functionality provided we're OK with a different granularity error message.

Treat as optional. I'll happily close if you'd prefer to keep as is.

[tzaffi]

FYI - my merges are about to repeat this work.

And optionally: Since you are returning out of the if's you can remove the else's and write the last 2 conditions as:

            if SubroutineDefinition._is_abi_annotation(ptype):
                return abi.type_spec_from_annotation(ptype)
            raise TealInputError(
                f"Function has parameter {parameter_name} of disallowed type {ptype}. "
                f"Only the types {(Expr, ScratchVar, 'ABI')} are allowed"
            )

[michaeldiamant]

Closing - #310 brings the same change in.