Reland "Vulkan: Implement GL_EXT_multi_draw_indirect"

This is a reland of 79f9d163b4
* Added drawcount > 1 as a condition to fall back to
MultiDraw*IndirectGeneral().
* Expanded the tests to include cases with disabled support
for multiDrawIndirect.

Original change's description:
> Vulkan: Implement GL_EXT_multi_draw_indirect
>
> * Optimized the implementations of multiDrawArraysIndirect()
> and multiDrawElementsIndirect() for Vulkan
>   * Added helper functions to support drawArraysIndirect() and
> drawElementsIndirect() as special cases of multiDraw*Indirect
> functions.
>   * Added the flag to enable the multiDrawIndirect feature
> (drawCount > 1). The generic implementation is used if the
> flag is disabled.
>
> Bug: angleproject:6439
> Change-Id: Ibc653d93d355657f828de9c33da22428629e450f
> Reviewed-on: https://chromium-review.googlesource.com/c/angle/angle/+/3276044
> Commit-Queue: Amirali Abdolrashidi <abdolrashidi@google.com>
> Reviewed-by: Shahbaz Youssefi <syoussefi@chromium.org>
> Reviewed-by: Jamie Madill <jmadill@chromium.org>

Bug: angleproject:6439
Change-Id: I96c015855fabc8abbb87320a5ca71a8d92d61954
Reviewed-on: https://chromium-review.googlesource.com/c/angle/angle/+/3313412
Reviewed-by: Jamie Madill <jmadill@chromium.org>
Reviewed-by: Shahbaz Youssefi <syoussefi@chromium.org>
Commit-Queue: Amirali Abdolrashidi <abdolrashidi@google.com>

util/EGLWindow.cpp

@@ -245,6 +245,15 @@ bool EGLWindow::initializeDisplay(OSWindow *osWindow,
         disabledFeatureOverrides.push_back("supportsViewportFlip");
     }
 
+    if (params.supportsVulkanMultiDrawIndirect == EGL_TRUE)
+    {
+        enabledFeatureOverrides.push_back("supportsMultiDrawIndirect");
+    }
+    else if (params.supportsVulkanMultiDrawIndirect == EGL_FALSE)
+    {
+        disabledFeatureOverrides.push_back("supportsMultiDrawIndirect");
+    }
+
     switch (params.emulatedPrerotation)
     {
         case 90: