Validate all type ids. (#1868)

* Validate all type ids.

The validator does not check if the type of an instruction is actually
a type unless the OpCode has a specific requirement.  For example,
OpFAdd is checked, but OpUndef is not.

The commit add a generic check that if there is a type id then the id
defines a type.

http://crbug.com/876694

* Merge other checks for type into new one.

There are a couple check that the type id is a type for specific
opcodes.  Those have been mereged into 1.

Small changes to other test cases to make them valid enough for the
purpose of the test.