Zygote: add a way to preload Vulkan driver

Since HWUI render pipeline has both GL and Vulkan backends now, we'd
like to preload either GL or Vulkan driver based upon HWUI's choice on
the render backend.

1) Keep using ro.zygote.disable_gl_preload property to disable Vulkan
driver preloading if HWUI's render pipeline uses Vulkan backend.
Properly rename the corresponding APIs for driver preloading.

2) Add a path to preload Vulkan driver based on HWUI's render backend.

Bug: 131249898
Test: build, flash and boot.
Test: verified with set USE_VULKAN=true
Test: verified with setprop debug.hwui.renderer skiagl/skiavk
Change-Id: Ie0bf5d18edcf907c75a25ac3249e2620ec21b63c