🔗 Go feature: Modernized Go fix

The go fix is re-implemented using the Go analysis framework — the same one go vet uses.

While go fix and go vet now use the same infrastructure, they have different purposes and use different sets of analyzers:

• Vet is for reporting problems. Its analyzers describe actual issues, but they don't always suggest fixes, and the fixes aren't always safe to apply.
• Fix is (mostly) for modernizing the code to use newer language and library features. Its analyzers produce fixes are always safe to apply, but don't necessarily indicate problems with the code.

See the full set of fix's analyzers in the Analyzers section.