refactor: retry file remove/rename when a file is busy and clean up os detection (#38588)

Rename functions "util.Remove" (remove.go) to "util.RemoveWithRetry"
(file_retry.go) and add comments to clarify their behaviors, also add
tests.

Refactor callers: when no concurrent access (cmd cli, migration, app
init, test), use "os.Xxx" directly.

More details are in `modules/util/file_retry.go`

By the way, clean up OS (windows) detection, make FileURLToPath test
always run

cmd/dump.go

@@ -198,7 +198,7 @@ func runDump(ctx context.Context, cmd *cli.Command) error {
 		}
 		defer func() {
 			_ = dbDump.Close()
-			if err := util.Remove(dbDump.Name()); err != nil {
+			if err := os.Remove(dbDump.Name()); err != nil {
 				log.Warn("Unable to remove temporary file: %s: Error: %v", dbDump.Name(), err)
 			}
 		}()

cmd/embedded.go

@@ -18,7 +18,6 @@ import (
 	"gitea.dev/modules/public"
 	"gitea.dev/modules/setting"
 	"gitea.dev/modules/templates"
-	"gitea.dev/modules/util"
 
 	"github.com/urfave/cli/v3"
 )
@@ -255,7 +254,7 @@ func extractAsset(d string, a assetFile, overwrite, rename bool) error {
 	} else if !fi.Mode().IsRegular() {
 		return fmt.Errorf("%s already exists, but it's not a regular file", dest)
 	} else if rename {
-		if err := util.Rename(dest, dest+".bak"); err != nil {
+		if err := os.Rename(dest, dest+".bak"); err != nil {
 			return fmt.Errorf("error creating backup for %s: %w", dest, err)
 		}
 		// Attempt to respect file permissions mask (even if user:group will be set anew)