Unregister non-matching serviceworkers (#15834)

* Unregister non-matching serviceworkers

With the addition of the /assets url, users who visited a previous
version of the site now may have two active service workers, one with
the old scope `/` and one with scope `/assets`. This check for
serviceworkers that do not match the current script path and unregisters
them.

Also included is a small refactor to publicpath.js which was simplified
because AssetUrlPrefix is always present now. Also it makes use of the
new joinPaths helper too.

Fixes: https://github.com/go-gitea/gitea/pull/15823

models/user.go

@@ -789,6 +789,7 @@ var (
 		"debug",
 		"error",
 		"explore",
+		"favicon.ico",
 		"ghost",
 		"help",
 		"install",
@@ -807,10 +808,10 @@ var (
 		"repo",
 		"robots.txt",
 		"search",
+		"serviceworker.js",
 		"stars",
 		"template",
 		"user",
-		"favicon.ico",
 	}
 
 	reservedUserPatterns = []string{"*.keys", "*.gpg"}