LibWeb: Split the WebAssemblyInstance object logic into multiple files

Now that we're adding a constructor to it, let's split it up like the
rest of LibWeb does.

Userland/Libraries/LibWeb/CMakeLists.txt

@@ -222,10 +222,11 @@ set(SOURCES
     UIEvents/EventNames.cpp
     UIEvents/MouseEvent.cpp
     URLEncoder.cpp
+    WebAssembly/WebAssemblyInstanceObject.cpp
+    WebAssembly/WebAssemblyInstanceObjectPrototype.cpp
     WebAssembly/WebAssemblyMemoryConstructor.cpp
     WebAssembly/WebAssemblyMemoryPrototype.cpp
     WebAssembly/WebAssemblyObject.cpp
-    WebAssembly/WebAssemblyObjectPrototype.cpp
     WebContentClient.cpp
     XHR/EventNames.cpp
     XHR/XMLHttpRequest.cpp