x/tools/gopls: improve FixImports filter for short dangling references #67889
Description
@dominikh reports in slack that gopls' organizeImports is particularly slow when there is a method call on an undefined symbol, often when the symbol is short.
Coincidentally, I was just looking at this logic, and noticed that it would lead to a LOT of additional candidates for short unresolved references. For example a single selector on an undefined 'e' or 's' may require reading a large chunk of the module cache.
This should be straightforward to reproduce, if so, and probably not too hard to fix. Unfortunately, I suspect that the imprecise heuristic probably avoids some edge cases like gopkg.in paths, but even so we can handle those explicitly.