feat: add redundant-build-tag rule

[alexandear]

This PR adds redundant-build-tag that suggests removing // +build lines when //go:build is present.

According to the "Build constraints":

Go versions 1.16 and earlier used a different syntax for build constraints, with a "// +build" prefix. The gofmt command will add an equivalent //go:build constraint when encountering the older syntax.

But gofmt doesn't automatically remove // +build lines.

[ccoVeille]

Good idea. I'm unsure about the rule name, but it's a good thing.

[ccoVeille]

Did you check if gostrict or go vet wasn't providing something equivalent?

EDIT: I just checked, nothing detects it currently.

It's funny because I reported something about it a few days ago
gofr-dev/gofr#1175

@alexandear How did you find out the ``// +build:` directive ?

[alexandear]

@alexandear How did you find out the ``// +build:` directive ?

I found // +build by reading the release notes for Go 1.18. Later, while reading the Go source, I came across go fix, which has a fix named buildtag. The command go fix -fix buildtag ./... removes old build tags across the codebase.

Here are my PRs that fix build tags:

• all: go fix -fix buildtag chromedp/chromedp#1274
• all: remove obsolete build tags go-delve/delve#3513
• chore: Remove +build comments from modules twpayne/chezmoi#2846
• Delete obsolete // +build lines otiai10/copy#137

[alexandear]

Renamed to redundant-build-tag.

In the future, this rule can be extended with functionality to find redundant build tags like in this PR go-delve/delve#3556

[ccoVeille]

Renamed to redundant-build-tag.

In the future, this rule can be extended with functionality to find redundant build tags like in this PR go-delve/delve#3556

Maybe you could open an issue to keep track of the idea