build: modernize Go usage

This commit modernizes Go usage. This was done with:

go run golang.org/x/tools/gopls/internal/analysis/modernize/cmd/modernize@latest -fix -test ./...

Then files needed to be `go fmt`ed and a few comments needed to be
restored.

The modernizations include replacing

- if/else conditional assignment by a call to the built-in min or max functions added in go1.21
- sort.Slice(x, func(i, j int) bool) { return s[i] < s[j] } by a call to slices.Sort(s), added in go1.21
- interface{} by the 'any' type added in go1.18
- append([]T(nil), s...) by slices.Clone(s) or slices.Concat(s), added in go1.21
- loop around an m[k]=v map update by a call to one of the Collect, Copy, Clone, or Insert functions from the maps package, added in go1.21
- []byte(fmt.Sprintf...) by fmt.Appendf(nil, ...), added in go1.19
- append(s[:i], s[i+1]...) by slices.Delete(s, i, i+1), added in go1.21
- a 3-clause for i := 0; i < n; i++ {} loop by for i := range n {}, added in go1.22

backend/local/local.go

@@ -1046,7 +1046,7 @@ you can try to change the output.`,
 // The result should be capable of being JSON encoded
 // If it is a string or a []string it will be shown to the user
 // otherwise it will be JSON encoded and shown to the user like that
-func (f *Fs) Command(ctx context.Context, name string, arg []string, opt map[string]string) (interface{}, error) {
+func (f *Fs) Command(ctx context.Context, name string, arg []string, opt map[string]string) (any, error) {
 	switch name {
 	case "noop":
 		if txt, ok := opt["error"]; ok {
@@ -1056,7 +1056,7 @@ func (f *Fs) Command(ctx context.Context, name string, arg []string, opt map[str
 			return nil, errors.New(txt)
 		}
 		if _, ok := opt["echo"]; ok {
-			out := map[string]interface{}{}
+			out := map[string]any{}
 			out["name"] = name
 			out["arg"] = arg
 			out["opt"] = opt