QmlJS: Reactivate instantiating component scope detection.

* Bind::usesQmlPrototype is now significantly more performant
* type environments are no longer hashed by filename, but rather
  by Document *
* duplicate scope builds are avoided

Task-number: QTCREATORBUG-2835
Reviewed-by: Erik Verbruggen

src/libs/qmljs/qmljsscopebuilder.cpp

@@ -97,6 +97,11 @@ void ScopeBuilder::pop()
 void ScopeBuilder::initializeScopeChain()
 {
     ScopeChain &scopeChain = _context->scopeChain();
+    if (scopeChain.qmlComponentScope
+            && scopeChain.qmlComponentScope->document == _doc) {
+        return;
+    }
+
     scopeChain = ScopeChain(); // reset
 
     Interpreter::Engine *engine = _context->engine();