Render thread (also the main thread for some platforms) is blocked most of the time

[ryantrem]

Describe the bug
The Start/Finish calls are in the wrong order, and this results in the render thread to be in a blocked state rather than an idle state between frames being rendered. This severely limits how much work can be done on the render thread when a frame is not being actively rendered. In some cases (such as Android), the render thread is the same as the main UI thread. The net result is that UI can be laggy and unresponsive while an EngineView is active (since the thread spends much of its time in a blocked state).

From BabylonNative.cpp:

g_graphics->StartRenderingCurrentFrame();
g_update->Start();
g_update->Finish();
g_graphics->FinishRenderingCurrentFrame();

This ordering should be swapped. In the past, there were some problems with this, but maybe those issues have since been fixed.

To Reproduce
Profile while Babylon Native is rendering and observe that the render thread is in a blocked state for a significant amount of time during app execution.

Expected behavior
The render thread should be idle between frames and other work should be able to happen on the render thread.

Screenshots
I haven't profiled this in a while so I don't have screenshots or other evidence available.

Other

• Platform: [Definitely Android, maybe other platforms too.]

[ryantrem]

Oh looks like there is an existing issue on this: #343