OpenGL: let eglext_angle.h include eglext.h for platform

EGLStreamKHR and EGLDeviceEXT used by eglext_angle.h is undefined
without eglext.h. From the description of eglext_angle.h, it's just
for patching eglext.h and should never be explictly included. However,
eglext.h is generated from EGL spec. So we'd better not manually modify
eglext.h to include eglext_angle.h at the bottom. This change just let
eglext_angle.h include eglext.h.

Bug: 158235687
Test: build, flash and boot
Change-Id: I02f992d880cce41b3ddc70fb5a28a87a64f05ec7
diff --git a/opengl/include/EGL/eglext_angle.h b/opengl/include/EGL/eglext_angle.h
index 0556ea1..1f1bcb3 100644
--- a/opengl/include/EGL/eglext_angle.h
+++ b/opengl/include/EGL/eglext_angle.h
@@ -4,12 +4,12 @@
 // found in the LICENSE file.
 //
 // eglext_angle.h: ANGLE modifications to the eglext.h header file.
-//   Currently we don't include this file directly, we patch eglext.h
-//   to include it implicitly so it is visible throughout our code.
 
 #ifndef INCLUDE_EGL_EGLEXT_ANGLE_
 #define INCLUDE_EGL_EGLEXT_ANGLE_
 
+#include <EGL/eglext.h>
+
 // clang-format off
 
 #ifndef EGL_ANGLE_robust_resource_initialization