Similar to https://reviews.llvm.org/D140896, this adds deduction guides for the
counterpart of ArrayRef: MutableArrayRef. The update plan is the following:
- Add deduction guides for MutableArrayRef.
- Change uses in-tree from makeMutableArrayRef to use deduction guides
- Mark makeMutableArrayRef as deprecated for some time before removing to give downstream users time to update.
The deduction guides are similar to those provided by the makeMutableArrayRef
function templates, except we don't need one explicitly from MutableArrayRef.
I don't think this is going to be a n-op : it's going to call the copy constructor.