This reverts commit d0906276.

Reason for revert: Fixed parent CL

Original change's description:
> Revert "Vulkan: Generate xfb support code in SPIR-V for extension path"
>
> This reverts commit d06feeac.
>
> Reason for revert:
> Earlier CL breaks pre-rotation:
> https://chromium-review.googlesource.com/c/angle/angle/+/2598584
>
> Original change's description:
> > Vulkan: Generate xfb support code in SPIR-V for extension path
> >
> > The only piece of code that's needed to be generated for the extension
> > path is the following, at the right spot (right before depth correction
> > and pre-rotation):
> >
> >     ANGLEXfbPosition = gl_Position;
> >
> > The SPIR-V transformer already has gl_Position loaded for depth
> > correction and pre-rotation, so this change simply adds an OpStore to
> > ANGLEXfbPosition.
> >
> > As a result of this change, @@ XFB-OUT @@ is no longer emitted if
> > the transform feedback extension is supported.  With the above code now
> > placed correctly for geometry shaders, transform feedback tests for
> > geometry shaders are enabled.
> >
> > Bug: angleproject:3606
> > Change-Id: I13a7956ab62a1a6b4196ff999442b99b50226c0f
> > Reviewed-on: https://chromium-review.googlesource.com/c/angle/angle/+/2617659
> > Commit-Queue: Shahbaz Youssefi <syoussefi@chromium.org>
> > Reviewed-by: Charlie Lao <cclao@google.com>
> > Reviewed-by: Jamie Madill <jmadill@chromium.org>
>
> TBR=syoussefi@chromium.org,jmadill@chromium.org,cclao@google.com
>
> Change-Id: I74fa9fafe3c922cdb7cd09ee6351534e38528da9
> No-Presubmit: true
> No-Tree-Checks: true
> No-Try: true
> Bug: angleproject:3606
> Reviewed-on: https://chromium-review.googlesource.com/c/angle/angle/+/2634048
> Reviewed-by: Tim Van Patten <timvp@google.com>
> Commit-Queue: Tim Van Patten <timvp@google.com>

TBR=timvp@google.com,syoussefi@chromium.org,jmadill@chromium.org,cclao@google.com

# Not skipping CQ checks because this is a reland.

Bug: angleproject:3606
Change-Id: Ic49a0be10cdb58e2b47896554f272093e24f93b4
Reviewed-on: https://chromium-review.googlesource.com/c/angle/angle/+/2633711
Commit-Queue: Shahbaz Youssefi <syoussefi@chromium.org>
Reviewed-by: Shahbaz Youssefi <syoussefi@chromium.org>