Break accidental references in Parser::__clone

If you have a reference *to* an object field (anywhere in the call
stack) when you clone the object, the field will be cloned as a
reference rather than as a value.

So we have to break those unexpected references in the cloned object
manually, which is easy enough by making a non-reference copy and then
rebinding the cloned object's reference to this copy.

Bug: 56226
Change-Id: I9c600e9c0845b4fde0366126ce3809d74e2240b4
Merge "Break accidental references in Parser::__clone"