Check for mutability better (#127843)

This PR adds a function to determine if a type "looks" mutable. Since
it's impossible to be totally sure if something can or can't be modified
in C++, this makes a best-effort attempt to determine if variables of
that type can be modified or not.

The motivation for this change is the -Wunique-object-duplication
warning, which had a false positive due to a missed case while checking
for mutability. Pulling the logic into a separate function allows it to
be written much more cleanly. There should be no behavior change, except
that we no longer report function references to be mutable.

0 files changed, 0 insertions, 0 deletions