using gofmt and go vet in sh_test rules

We have a few lint-style checks for `gofmt` and `go vet` which are implemented as `sh_test`s. We had a `data` dependency on `@io_bazel_rules_go_toolchain//:toolchain`, which brought `external/io_bazel_rules_go_toolchain/bin` into the runfiles for the test, but with the recent refactoring, the `:toolchain` target no longer exists.

I tried updating this to `:go_toolchain`, but that doesn't seem to include any of the Go toolchain in the test runfiles anymore.

Is there a way we can depend on the Go toolchain from outside the `rules_go` repository? I've tried searching through the changes, but I'm having trouble figuring out if this is supposed to be possible.

cc @spxtr

Start by tracing the sh_test data dependencies and the refactored rules_go toolchain targets, then inspect which runfiles are provided by :go_toolchain from outside the rules_go repository. Done means the gofmt and go vet sh_tests can access the required Go toolchain through a supported external dependency.

Written by the indexing model from the issue text.