5758: SSR: Explicitly autoderef and ref placeholders as needed r=matklad a=davidlattimore
Structural search replace now inserts *, & and &mut in the replacement to match any auto[de]ref in the matched code.
e.g. `$a.foo() ==>> bar($a)` might convert `x.foo()` to `bar(&mut x)`
Co-authored-by: David Lattimore <dml@google.com>
