Add a new system property persist.graphics.egl

This new system property will be read and written
by a new developer option switch, through gpuservice.

Based on the value stored in persis.graphics.egl,
we will load different GLES driver.

e.g.
persist.graphics.egl == $ro.hardware.egl: load native GLES driver
persist.graphics.egl == angle: load angle as GLES driver

Bug: b/270994705
Test: m; flash and check Pixel 7 boots fine
Change-Id: Idec4b947d0c69c52cd798df4f834053bd306cf5f
diff --git a/private/property_contexts b/private/property_contexts
index 603c70b..f19ae0c 100644
--- a/private/property_contexts
+++ b/private/property_contexts
@@ -1389,6 +1389,7 @@
 
 graphics.gpu.profiler.support          u:object_r:graphics_config_prop:s0 exact bool
 graphics.gpu.profiler.vulkan_layer_apk u:object_r:graphics_config_prop:s0 exact string
+persist.graphics.egl             u:object_r:graphics_config_writable_prop:s0 exact string
 
 ro.cpuvulkan.version u:object_r:graphics_config_prop:s0 exact int