clang: fix -Wsign-conversion errors

Cast some values as their unsigned equivalents or `size_t` to match the
parameter type used for the template object under test. Also, provide
UInt32 equivalent delegate methods for some callers (with
int-equivalents for backwards compatibility).

This closes #2146.

Signed-off-by: Enji Cooper <yaneurabeya@gmail.com>

googletest/include/gtest/internal/gtest-internal.h

@@ -700,7 +700,7 @@ class TypeParameterizedTest {
     // list.
     MakeAndRegisterTestInfo(
         (std::string(prefix) + (prefix[0] == '\0' ? "" : "/") + case_name +
-         "/" + type_names[index])
+         "/" + type_names[static_cast<size_t>(index)])
             .c_str(),
         StripTrailingSpaces(GetPrefixUntilComma(test_names)).c_str(),
         GetTypeName<Type>().c_str(),