Refactor public interface to be less strict C and more python friendly

* Generally this means removing ref out parameters and instead returning
  values. In a couple of cases we will want to avoid copies in future
  either by returning const references (e.g. to the pipeline state which
  is immutable).
* At the same time, some pointless bool return values that were always
  true and didn't indicate errors have been removed. They can be added
  again if an error condition comes back.
* Some free functions still have out parameters as C linkage doesn't
  allow returning user types by value.
* The C# UI still invokes into C wrappers for all the C++ classes, which
  handle taking the return value and doing a copy into an out parameter
  still for compatibility.

qrenderdoc/Windows/EventBrowser.cpp

@@ -263,10 +263,7 @@ void EventBrowser::on_timeDraws_clicked()
 {
   m_Ctx.Renderer().AsyncInvoke([this](IReplayRenderer *r) {
 
-    GPUCounter counters[] = {GPUCounter::EventGPUDuration};
-
-    rdctype::array<CounterResult> results;
-    r->FetchCounters(counters, 1, &results);
+    rdctype::array<CounterResult> results = r->FetchCounters({GPUCounter::EventGPUDuration});
 
     GUIInvoke::call([this, results]() { SetDrawcallTimes(ui->events->topLevelItem(0), results); });
   });