[mlir][Parser] Make parse{Attribute,Type} null-terminate input

`parseAttribute` and `parseType` require null-terminated strings as
input, but this isn't great considering the argument type is
`StringRef`. This changes them to copy to a null-terminated buffer by
default, with a `isKnownNullTerminated` flag added to disable the
copying.

closes #58964

Reviewed By: rriddle, kuhar, lattner

Differential Revision: https://reviews.llvm.org/D145182

mlir/lib/Bytecode/Reader/BytecodeReader.cpp

@@ -1031,9 +1031,11 @@ 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, /*isKnownNullTerminated=*/true);
   else
-    result = ::parseAttribute(asmStr, context, Type(), &numRead);
+    result = ::parseAttribute(asmStr, context, Type(), &numRead,
+                              /*isKnownNullTerminated=*/true);
   if (!result)
     return failure();