This patch fixes TypeInfo.GetVTable so that it specializes the vtable
for generic type instances. Also fix a minor bug in PropertyInfo that
would pass null pointers to GetMethodByDefinition.
Per the C# language reference
(https://docs.microsoft.com/en-us/dotnet/csharp/language-reference/language-specification/basic-concepts#hiding-through-inheritance):
> The rules governing operator declarations (Operators) make it
> impossible for a derived class to declare an operator with the same
> signature as an operator in a base class. Thus, operators never hide
> one another.
Therefore, new is not necessary or permitted on operators, even if the
method signatures are identical. This situation can arise if, for
example, an explicit conversion operator from the same target class
exists in both a base class and a derived class.
Bug #1 is that in 32-bit programs, typeDefinitionIndex might be
0xffff_ffff_ffff_ffff instead (32-bit -1 sign-extended to 64 bits), so
we fix that by simply masking to get the low 32 bits.
Bug #2 is that, if the TypeRef points to no generic instance, we return
null, which wasn't being checked for in the IDAPythonScript generator.
Since that's the only time we could get a null type in Types, we simply
remove nulls from the Types collection.
This basically finishes the concrete generics implementation. We can now
enumerate all members of a concrete generic type with full type
substitution implemented.
Also add a simple test to verify that we can obtain the correct type for
a field of a concrete generic type.
Now that we generate methods in instantiated generic types, we were
getting test failures from methods that were being detected as new
methods. In actuality, they weren't new, but they differed only in
generic type parameters from some base type method, and
GetSignatureString ignores generic parameters completely.
This fix eliminates the hacky GetSignatureString and replaces it with
more-or-less proper signature comparison. This even manages to fix an
incorrect test case from Methods.cs (because GetSignatureString was
incorrectly incorporating the return type - when the return type should
not be examined for signature checking).
