Make resources fetched via resources.Get and similar language agnostic

With the newly released Hugo Pipes, resources fetched and processed via `resources.Get` and similar was published to the relevant language sub folder when in multilingual mode.

The thought behind that was maximum flexibility with support for `assetDir` per language.

In practice this was a bad idea:

* You get duplication of identical content, with added processing time
* You end up with path issues that seem to be hard to find a way around (`@fa-font-path` is one example)

This commit changes that. Now there is only one `assetDir` and if you, as one example, need to generate a CSS per langugage, you need to set the paths yourself.

Fixes #5017

langs/language.go

@@ -33,6 +33,8 @@ var globalOnlySettings = map[string]bool{
 	strings.ToLower("defaultContentLanguageInSubdir"): true,
 	strings.ToLower("defaultContentLanguage"):         true,
 	strings.ToLower("multilingual"):                   true,
+	strings.ToLower("assetDir"):                       true,
+	strings.ToLower("resourceDir"):                    true,
 }
 
 // Language manages specific-language configuration.