Raise priority of RenderThread early during startup

Instead of raising the RenderThread priority after earlyPreloadGLContext is finished, retrieve the tid of the render thread while preloading and apply the priority boost to the RenderThread as soon as possible.

Flag: android.app.early_render_thread_priority_boost
Bug: 417909658
Change-Id: I82d7f131b16472a93622f31c8b906ae3695a18be