HackStudio: Add ClassView tab for viewing classes in a tree structure

This enables the user to view and navigate classes with a TreeView that
is updated by the LanguageServer as it parses the code.

It offers a new neat way to view the project's structure :^)

Userland/Libraries/LibGUI/AutocompleteProvider.h

@@ -61,6 +61,8 @@ public:
         String file;
         size_t line { 0 };
         size_t column { 0 };
+
+        bool operator==(const ProjectLocation&) const;
     };
 
     enum class DeclarationType {
@@ -78,6 +80,8 @@ public:
         ProjectLocation position;
         DeclarationType type;
         String scope;
+
+        bool operator==(const Declaration&) const;
     };
 
     virtual void provide_completions(Function<void(Vector<Entry>)>) = 0;