compute: strip whitespace around arrow syntax
Created by: rvantonder
Stacked on https://github.com/sourcegraph/sourcegraph/pull/26542.
As in title. Just a convenience change so that stuff like a -> b
, a->b
, a-> b
is all fine and doesn't borrow whitespace from the search pattern. Later will have to add a scanner to escape/disambiguate left and right hand sides but this is not a major focus right now.