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/sharefile/sharefile.go

@@ -537,7 +537,7 @@ func NewFs(ctx context.Context, name, root string, m configmap.Mapper) (fs.Fs, e
 // Fill up (or reset) the buffer tokens
 func (f *Fs) fillBufferTokens() {
 	f.bufferTokens = make(chan []byte, f.ci.Transfers)
-	for i := 0; i < f.ci.Transfers; i++ {
+	for range f.ci.Transfers {
 		f.bufferTokens <- nil
 	}
 }

backend/sharefile/upload.go

@@ -57,10 +57,7 @@ func (f *Fs) newLargeUpload(ctx context.Context, o *Object, in io.Reader, src fs
 		return nil, fmt.Errorf("can't use method %q with newLargeUpload", info.Method)
 	}
 
-	threads := f.ci.Transfers
-	if threads > info.MaxNumberOfThreads {
-		threads = info.MaxNumberOfThreads
-	}
+	threads := min(f.ci.Transfers, info.MaxNumberOfThreads)
 
 	// unwrap the accounting from the input, we use wrap to put it
 	// back on after the buffering