cue/format: sort imports

[mezuzza]

Currently, cue fmt doesn't seem to build out a canonical ordering for imports. It makes it slightly annoying to look at the top of a file with a number of imports to see what is being used.

As far as I can tell, the ordering of the imports within the import statement has no bearing on the evaluated result, so it seems like this would be a nice way to increase the consistency of the experience.

Prior art here:
Javascript ecosystem uses prettier which doesn't sort imports but javascript has side effects on import
Similar issue with python and black.

Both support other tools (import sort plugin and isort respectively) which handle import sorting and grouping for you.

Go has go fmt which doesn't handle imports, but also supports goimports.

Clang-format supports sorting with options.

[mvdan]

I agree this is a good idea, and in fact we have some code for it but it's currently unused.