TASK: Fusion clean up the usages how @process adds css classes.

with: neos/flow-development-collection#2710

we can add any scalar types to Array.push as base, which will be auto casted to an array:
`Array.push("foo", "bar")`
which results in -> `["foo", "bar"]`
which is rendered as `foo bar`

previously we had to cast it to an array beforehand. I integrated this for the 'neos-contentcollection' once: neos/neos-development-collection#3438 - but this cleans the manual cast up.

(this also fixes any real low level css class adding via `Type.isString()` etc by just casting to an array and then pushing the new value.)

Also the last use of copy will be removed, by manually copying the (now little) code over.
fixes: neos/neos-development-collection#3588

Resources/Private/Fusion/Prototypes/Content.fusion

@@ -18,18 +18,9 @@ prototype(Neos.Neos:Content) < prototype(Neos.Fusion:Template) {
   #   attributes.class.@process.nodeType >
   # }
   # in your site's Fusion if you don't need that behavior.
-  attributes.class.@process.nodeType = Neos.Fusion:Case {
-    @context.nodeTypeClassName = ${String.toLowerCase(String.pregReplace(node.nodeType.name, '/[[:^alnum:]]/', '-'))}
-
-    classIsString {
-      condition = ${Type.isString(value)}
-      renderer = ${String.trim(String.trim(value) + ' ' + nodeTypeClassName)}
-    }
-
-    classIsArray {
-      condition = ${Type.isArray(value)}
-      renderer = ${Array.push(value, nodeTypeClassName)}
-    }
+  attributes.class.@process.nodeType = Neos.Fusion:Value {
+    nodeTypeClassName = ${String.toLowerCase(String.pregReplace(node.nodeType.name, '/[[:^alnum:]]/', '-'))}
+    value = ${Array.push(value, this.nodeTypeClassName)}
   }
 
   # The following line must not be removed as it adds required meta data to all content elements in backend

Resources/Private/Fusion/Prototypes/ContentCollection.fusion

@@ -25,10 +25,7 @@ prototype(Neos.Neos:ContentCollection) < prototype(Neos.Fusion:Tag) {
   #   attributes.class.@process.collectionClass >
   # }
   attributes {
-    class.@process.collectionClass = Neos.Fusion:Value {
-      castedArray = ${Type.isArray(value) ? value : [value]}
-      value = ${Array.push(this.castedArray, 'neos-contentcollection')}
-    }
+    class.@process.collectionClass = ${Array.push(value, 'neos-contentcollection')}
     data-__neos-insertion-anchor = true
     data-__neos-insertion-anchor.@if.onlyRenderInBackend = ${node.context.inBackend && node.context.currentRenderingMode.edit}
   }

Resources/Private/Fusion/Prototypes/Page.fusion

@@ -63,19 +63,8 @@ prototype(Neos.Neos:Page) < prototype(Neos.Fusion:Http.Message) {
     @position = '20'
     tagName = 'body'
     omitClosingTag = true
-    attributes.class.@process.addNeosBackendClass = Neos.Fusion:Case {
-      @if.onlyRenderWhenNotInLiveWorkspace = ${documentNode.context.inBackend}
-
-      classIsString {
-        condition = ${Type.isString(value)}
-        renderer = ${String.trim(value + ' neos-backend')}
-      }
-
-      classIsArray {
-        condition = ${Type.isArray(value)}
-        renderer = ${Array.push(value, 'neos-backend')}
-      }
-    }
+    attributes.class.@process.addNeosBackendClass = ${Array.push(value, 'neos-backend')}
+    attributes.class.@process.addNeosBackendClass.@if.onlyRenderWhenNotInLiveWorkspace = ${documentNode.context.inBackend}
   }
 
   # Content of the body tag. To be defined by the integrator.