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/webdav/chunking.go

@@ -112,12 +112,8 @@ func (o *Object) uploadChunks(ctx context.Context, in0 io.Reader, size int64, pa
 			return err
 		}
 
-		contentLength := chunkSize
-
 		// Last chunk may be smaller
-		if size-offset < contentLength {
-			contentLength = size - offset
-		}
+		contentLength := min(size-offset, chunkSize)
 
 		endOffset := offset + contentLength - 1
 

backend/webdav/odrvcookie/fetch.go

@@ -185,7 +185,7 @@ func (ca *CookieAuth) getSPToken(ctx context.Context) (conf *SharepointSuccessRe
 	if err != nil {
 		return nil, err
 	}
-	reqData := map[string]interface{}{
+	reqData := map[string]any{
 		"Username":   ca.user,
 		"Password":   ca.pass,
 		"Address":    ca.endpoint,