Vulkan: Restore CommandBuffer to namespace vk

Moved vk::CommandBuffer and vk::SecondaryCommandBuffer to vk::priv:: and
aliased vk::CommandBuffer to one or the other.  This allows the rest of
the classes to continue seeing vk::CommandBuffer as they used to do.
Used a special alias for the primary command buffer that gets submitted
(vk::PrimaryCommandBuffer).

Bug: angleproject:3136
Change-Id: I61236fd182230991db7395d05e3da3be5e3f45be
Reviewed-on: https://chromium-review.googlesource.com/c/angle/angle/+/1534456
Reviewed-by: Shahbaz Youssefi <syoussefi@chromium.org>
Commit-Queue: Shahbaz Youssefi <syoussefi@chromium.org>
diff --git a/src/libANGLE/renderer/vulkan/ProgramVk.cpp b/src/libANGLE/renderer/vulkan/ProgramVk.cpp
index 64dccb7..206bc20 100644
--- a/src/libANGLE/renderer/vulkan/ProgramVk.cpp
+++ b/src/libANGLE/renderer/vulkan/ProgramVk.cpp
@@ -862,7 +862,7 @@
             // Ensure the image is in read-only layout
             if (image.isLayoutChangeNecessary(vk::ImageLayout::FragmentShaderReadOnly))
             {
-                CommandBufferT *srcLayoutChange;
+                vk::CommandBuffer *srcLayoutChange;
                 ANGLE_TRY(image.recordCommands(contextVk, &srcLayoutChange));
 
                 image.changeLayout(VK_IMAGE_ASPECT_COLOR_BIT,
@@ -910,7 +910,8 @@
     }
 }
 
-angle::Result ProgramVk::updateDescriptorSets(ContextVk *contextVk, CommandBufferT *commandBuffer)
+angle::Result ProgramVk::updateDescriptorSets(ContextVk *contextVk,
+                                              vk::CommandBuffer *commandBuffer)
 {
     // Can probably use better dirty bits here.