Found two issues when native OVR_multiview and OVR_multiview2 extensions are generated.
1. OVR_multiview got replaced by the OVR_multiview2 in the translated shader (ESSL & GLSL)
2. Duplicate #extension OVR_multiview2 (for Fragment & Vertex) and 'layout (num_views=x)' (for Vertex) got generated into the translated shader.

Bug: angleproject:4247
Change-Id: I9a550883eeb326d95af4557578f8202a9493f4ec
Reviewed-on: https://chromium-review.googlesource.com/c/angle/angle/+/1983802Reviewed-by: Shahbaz Youssefi <syoussefi@chromium.org>
Reviewed-by: Rafael Cintron <rafael.cintron@microsoft.com>
Reviewed-by: Geoff Lang <geofflang@chromium.org>
Commit-Queue: Geoff Lang <geofflang@chromium.org>