rustc: Prevent repeated moves out of proc upvars

This fixes the categorization of the upvars of procs (represented internally
as once fns) to consider usage to require a loan. In doing so, upvars are no
longer allowed to be moved out of repeatedly in loops and such.

Closes #10398
Closes #12041
Closes #12127
auto merge of #13413 : alexcrichton/rust/once-fn-move, r=brson

This fixes the categorization of the upvars of procs (represented internally
as once fns) to consider usage to require a loan. In doing so, upvars are no
longer allowed to be moved out of repeatedly in loops and such.

Closes #10398
Closes #12041
Closes #12127