Remove separate ANGLE_texture_multisample_array

We can just expose OES_texture_storage_multisample_2d_array instead.
The compiler was already changed to accept
OES_texture_storage_multisample_2d_array, and now the change is made
also at the API level.

Out-of-bounds access guarantees provided by ANGLE were the only big
difference between the ANGLE spec and the OES spec, so it's simpler
to just expose the native extension. Safe out-of-bounds accesses can
be guaranteed without having them in the extension spec.

This also adds missing texStorage3DMultisample entry point to the proc
table, which will enable running dEQP tests.

BUG=angleproject:2775
TEST=angle_end2end_tests

Change-Id: Idf376ee877a3374a33de177df023f0531ec8f01d
Reviewed-on: https://chromium-review.googlesource.com/1196722
Reviewed-by: Corentin Wallez <cwallez@chromium.org>
Reviewed-by: Jamie Madill <jmadill@chromium.org>
Commit-Queue: Olli Etuaho <oetuaho@nvidia.com>
diff --git a/src/libANGLE/Context.cpp b/src/libANGLE/Context.cpp
index 29b5e46..f48bc8a 100644
--- a/src/libANGLE/Context.cpp
+++ b/src/libANGLE/Context.cpp
@@ -3159,7 +3159,7 @@
 
         // TODO(http://anglebug.com/2775): Multisample arrays could be supported on ES 3.0 as well
         // once 2D multisample texture extension is exposed there.
-        supportedExtensions.textureMultisampleArray = false;
+        supportedExtensions.textureStorageMultisample2DArray = false;
     }
 
     if (getClientVersion() > ES_2_0)