Fix image ref state when loading old captures

This fixes a performance regression when loading captures from <=v1.6
(before the new image state code went in). The code to import the old
image state information was incorrectly discarding the frame ref
information, forcing the images to be reinitialized on every replay.

In old captures `ImageRefs` chunk is processed, creating `ImageState`
objects that only contain `refType`; then `BeginCaptureFrame` processes
the `ImageLayouts` info, to construct a new `ImageState` object,
containing the layout information. This `ImageState` was overwriting the
`ImageState` from the `ImageRefs` chunk, discarding the `refType` info.
This change merges the `ImageState`s from `ImageRefs`, where each field
of the merged image state comes from whichever `ImageState` had a
non-undefined value for that field.

For new captures, this change should be safe, since the image state
should be undefined when the `BeginCaptureFrame` chunk is processed, so
the `MergCaptureBeginState` call will just take all the state fields
from the `ImageState` stored in the `BeginCaptureFrame` chunk.

Change-Id: Id2252edb6382bd02bc0236b77c7cca667e97bf29

renderdoc/driver/vulkan/vk_image_states.cpp

@@ -941,7 +941,7 @@ void ImageState::Merge(const ImageState &other, ImageTransitionInfo info)
 void ImageState::MergeCaptureBeginState(const ImageState &initialState)
 {
   oldQueueFamilyTransfers = initialState.oldQueueFamilyTransfers;
-  subresourceStates = initialState.subresourceStates;
+  subresourceStates.Merge(initialState.subresourceStates, ComposeFrameRefsFirstKnown);
   maxRefType = initialState.maxRefType;
 }