x/tools/go/analysis: add Config.GoVersion field

[rsc]

To fix #61174 and set up for future changes in Go 1.22, the go command needs to pass the Go version in the compiler config. This requires adding a new GoVersion string field to the Config struct and then passing it through to the types.Config for the package. The full diff is:

diff --git a/go/analysis/unitchecker/unitchecker.go b/go/analysis/unitchecker/unitchecker.go
index ff22d23ce..10c76bc62 100644
--- a/go/analysis/unitchecker/unitchecker.go
+++ b/go/analysis/unitchecker/unitchecker.go
@@ -62,6 +62,7 @@ type Config struct {
 	Compiler                  string
 	Dir                       string
 	ImportPath                string
+	GoVersion                 string // minimum required Go version, such as "go1.21.0"
 	GoFiles                   []string
 	NonGoFiles                []string
 	IgnoredFiles              []string
@@ -217,8 +218,9 @@ func run(fset *token.FileSet, cfg *Config, analyzers []*analysis.Analyzer) ([]re
 		return compilerImporter.Import(path)
 	})
 	tc := &types.Config{
-		Importer: importer,
-		Sizes:    types.SizesFor("gc", build.Default.GOARCH), // assume gccgo ≡ gc?
+		Importer:  importer,
+		Sizes:     types.SizesFor("gc", build.Default.GOARCH), // assume gccgo ≡ gc?
+		GoVersion: cfg.GoVersion,
 	}
 	info := &types.Info{
 		Types:      make(map[ast.Expr]types.TypeAndValue),

[gopherbot]

Change https://go.dev/cl/507976 mentions this issue: cmd/go: pass GoVersion in vet config

[gopherbot]

Change https://go.dev/cl/507880 mentions this issue: go/analysis: pass package's Go version to type checker

[rsc]

Based on the discussion above, this proposal seems like a likely accept.
— rsc for the proposal review group

[rsc]

No change in consensus, so accepted. 🎉
This issue now tracks the work of implementing the proposal.
— rsc for the proposal review group