Start RenderThread earlier to preload Vulkan/EGL drivers

This CL should fix application startup regression for Vulkan
detected by "Hermetic Startup: EmptyActivity" test.
EGL drivers are loaded in a temp thread to leave more time
in RenderThread for other work. Loading EGL drivers
on the RenderThread may cause a perf regression.

Test: Ran cold-dropcache-test test.
Bug: 122659224
Bug: 123361175
Change-Id: I8ca818e98fac196a41d079be15594caca5cb1bab