[mlir][AsmParser] Improve parse{Attribute,Type} error handling

Currently these functions report errors directly to stderr, this updates
them to use diagnostics instead. This also makes partially-consumed
strings an error if the `numRead` parameter isn't provided (the
docstrings already claimed this happened, but it didn't.)

While here I also tried to reduce the number of overloads by switching
to using default parameters.

Reviewed By: rriddle

Differential Revision: https://reviews.llvm.org/D144804

mlir/lib/Bytecode/Reader/BytecodeReader.cpp

@@ -1031,9 +1031,9 @@ LogicalResult AttrTypeReader::parseAsmEntry(T &result, EncodingReader &reader,
   size_t numRead = 0;
   MLIRContext *context = fileLoc->getContext();
   if constexpr (std::is_same_v<T, Type>)
-    result = ::parseType(asmStr, context, numRead);
+    result = ::parseType(asmStr, context, &numRead);
   else
-    result = ::parseAttribute(asmStr, context, numRead);
+    result = ::parseAttribute(asmStr, context, Type(), &numRead);
   if (!result)
     return failure();