*: sort all the imports

[benesch]

I'm submitting this PR as a starting point for discussion. I've added a new flag to crlfmt, -groupimports, that performs import sorting automatically. That way adventurous folks, like myself and @jordanlewis, can opt-in for a bit and see how many spurious diffs are generated in the normal course of development.

As I mentioned on Slack, think that teaching crlfmt to do this automatically will be a net positive. crlfmt is already picky enough about function signatures that I think most everyone has their editors configured to format automatically on save, or at least have a workflow that involves running crlfmt before pushing to TeamCity. If crlfmt is good enough at sorting imports, no one will ever think about import sorting again. That's not the case in the current "try not to worry about import sorting" state of affairs. I don't nit import sorting on code reviews, but I still end up wasting time sorting imports if I add/remove an import to a file with a mis-sorted list of imports—I just can't help it.

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Consistently sort all of our imports into three groups. The first group
contains stdlib imports. The second group contains third-party imports.
The third group contains imports cockroachdb imports.

This commit was automatically generated with crlfmt's new groupimports
feature. For now, to avoid burdening developers with extra CI cycles,
import sorting is not enforced by make lint. We may want to revist
this decision if the number of developers who configure their editors to
automatically group imports reaches critical mass.

Note that this import sorting is compatible with both gofmt and
goimports; that is, upon seeing this import sorting, neither gofmt nor
goimports will feel compelled to change it.

Release note: None

[cockroach-teamcity]

This change is 

[cockroach-teamcity]

This change is 

[benesch]

Whoops. I'll have to fix this.

[bdarnell]

Consistently sort all of our imports into three groups. The first group
contains stdlib imports. The second group contains third-party imports.
The third group contains imports cockroachdb imports.

I understand that having three groups with some imports in the "wrong" group is an eyesore. But I'd rather solve this by forbidding the third group than mandating it. Why keep cockroachdb imports separate?

[bdarnell]

Consistently sort all of our imports into three groups. The first group
contains stdlib imports. The second group contains third-party imports.
The third group contains imports cockroachdb imports.

I understand that having three groups with some imports in the "wrong" group is an eyesore. But I'd rather solve this by forbidding the third group than mandating it. Why keep cockroachdb imports separate?

[benesch]

But I'd rather solve this by forbidding the third group than mandating it.

Sure, that works for me.

[benesch]

But I'd rather solve this by forbidding the third group than mandating it.

Sure, that works for me.