drive: rewrite Location headers

This ensures that MOVE, LOCK and any other verbs that use the Location
header work correctly.

Fixes #11758

Signed-off-by: Percy Wegmann <percy@tailscale.com>

drive/driveimpl/shared/pathutil.go

@@ -4,6 +4,7 @@
 package shared
 
 import (
+	"net/url"
 	"path"
 	"strings"
 )
@@ -35,6 +36,16 @@ func Join(parts ...string) string {
 	return path.Join(fullParts...)
 }
 
+// JoinEscaped is like Join but path escapes each part.
+func JoinEscaped(parts ...string) string {
+	fullParts := make([]string, 0, len(parts))
+	fullParts = append(fullParts, sepString)
+	for _, part := range parts {
+		fullParts = append(fullParts, url.PathEscape(part))
+	}
+	return path.Join(fullParts...)
+}
+
 // IsRoot determines whether a given path p is the root path, defined as either
 // empty or "/".
 func IsRoot(p string) bool {