feat(di): provide two ways to create an injector, resolved and unresolved

Add two factory static functions to Injector: resolveAndCreate and
fromResolvedBindings.

We want to avoid resolution and flattening every time we create a new
injector. This commit allows the user to cache resolved bindings and
reuse them.

modules/benchmarks/src/element_injector/element_injector_benchmark.js

@@ -12,7 +12,7 @@ export function main() {
   var iterations = getIntParameter('iterations');
 
   reflector.reflectionCapabilities = new ReflectionCapabilities();
-  var appInjector = new Injector([]);
+  var appInjector = Injector.resolveAndCreate([]);
 
   var bindings = [A, B, C];
   var proto = new ProtoElementInjector(null, 0, bindings);