A recent change was introduced in goimports improving how it sort and
format imports in https://go-review.googlesource.com/c/tools/+/116795
This commit updates the vendored version of the golang.org/x/tools
repository to include these changes.
1. Support unparam linter and fix found issues
2. Replace forked mvdan.cc/lint and mvdan.cc/interfacer with the
upstream ones
3. Minimize forked megacheck: move the most of it's code to this repo
4. Use golang.org/x/tools/go/ssa import path instead of custom fork
paths
5. In golang.org/x/tools/go/{ssa,callgraph} use changed code from
honnef.co/go/tools
6. Add megacheck.check-unexported option: it found some issues in
the repo, fixed them all
