Add flag to move ANGLE binaries to /system/${LIB}. Previously ANGLE binaries were built into /vendor/${LIB}/egl, but since ANGLE is in AOSP and we would like to make sure shipping ANGLE is not blocked by vendor partition update, this patch moves ANGLE to /system/${LIB}. Relative path is eliminated as subdirectory is not preferred unless necessary. With the flag, if angle_on_system is set to true, then ANGLE libraries will be built into /system/${LIB}. Bug: b/293503000 Change-Id: I86448ca313bc4f66e1ca78e05797b02a3b8d318a Reviewed-on: https://chromium-review.googlesource.com/c/angle/angle/+/4996366 Reviewed-by: Cody Northrop <cnorthrop@google.com> Reviewed-by: Yuxin Hu <yuxinhu@google.com> Commit-Queue: Peiyong Lin <lpy@google.com>