applet_resource_user_id isn't actually modified and is just assigned to
a member variable, so this doesn't need to be a mutable reference.

Similarly, the device name itself isn't modified and is only moved. We
pass by value here, since we can still perform the move, but eliminate a
sneaky set of calls that can unintentionally destroy the original
string. Given how nested the calls are, it's good to get rid of this
potential vector for a use-after-move bug.

These don't affect class state, so we can mark them as such.

This function doesn't modify the passed in buffer, so we can make that
explicit.

Resolves a wackload of -Wdocumentation warnings due to mismatching tags
and whatnot.