Use packed enum for DrawElementsType.

The packing and unpacking take a few extra instructions. But it
completely obviates the need for any switches in the validation code.
Speed is slightly faster or the similar depending on the back-end.

Also add gl_angle_ext.xml to GL entry point generator inputs. This was
missing and would cause the code generation to miss certain changes.

Bug: angleproject:2985
Change-Id: I1ea41a71db71135000166ead8305ec42d22ff7b3
Reviewed-on: https://chromium-review.googlesource.com/c/1351729
Commit-Queue: Jamie Madill <jmadill@chromium.org>
Reviewed-by: Shahbaz Youssefi <syoussefi@chromium.org>
diff --git a/src/libANGLE/validationES3.cpp b/src/libANGLE/validationES3.cpp
index e33a2fd..fef519b 100644
--- a/src/libANGLE/validationES3.cpp
+++ b/src/libANGLE/validationES3.cpp
@@ -1413,7 +1413,7 @@
                                GLuint start,
                                GLuint end,
                                GLsizei count,
-                               GLenum type,
+                               DrawElementsType type,
                                const void *indices)
 {
     if (context->getClientMajorVersion() < 3)
@@ -3101,7 +3101,7 @@
 bool ValidateDrawElementsInstanced(Context *context,
                                    PrimitiveMode mode,
                                    GLsizei count,
-                                   GLenum type,
+                                   DrawElementsType type,
                                    const void *indices,
                                    GLsizei instanceCount)
 {
@@ -3152,7 +3152,7 @@
 bool ValidateMultiDrawElementsInstancedANGLE(Context *context,
                                              PrimitiveMode mode,
                                              const GLsizei *counts,
-                                             GLenum type,
+                                             DrawElementsType type,
                                              const GLvoid *const *indices,
                                              const GLsizei *instanceCounts,
                                              GLsizei drawcount)