Various fixes to make `model-viewer` example almost working. (#1801)

* Fixing `PseudoPtr` legalization and `gfx` lifetime issues.

* Fixing `model-viewer` example.

This change contains various fixes to bring `model-viewer` example to fully functional. These fixes include:
1. Add `spReflectionTypeLayout_getSubObjectRangeSpaceOffset` function to return the space index for a sub object referenced through a `ParameterBlock` binding.
2. Make sure `D3D12Device` specifies column major matrix order creating a Slang session.
3. Fix `platform::Window::close()` and `platform::Application::quit()`.
4. Fix memory leak during `model-viewer''s model loading.
5. Fix command buffer recording in `model-viewer`.

With these changes, model viewer can now produce an image with a gray cube. The lighting is still incorrect becuase the `gfx` shader object implementation still does not handle "pending layout" resulting from global existential parameters.

* Fix d3d12 root signature creation.

* Use row-major matrix layout in model-viewer

1 files changed, 12 insertions, 9 deletions

diff --git a/tools/platform/windows/win-window.cpp b/tools/platform/windows/win-window.cpp
index 0d80eda7b..a0175a911 100644
--- a/tools/platform/windows/win-window.cpp
+++ b/tools/platform/windows/win-window.cpp
@@ -294,6 +294,8 @@ void Application::run(Window* mainWindow, bool waitForEvents)
     while (!Win32AppContext::isTerminated)
     {
         doEventsImpl(waitForEvents);
+        if (Win32AppContext::isTerminated)
+            break;
         if (mainWindow)
         {
             mainWindow->events.mainLoop();
@@ -343,14 +345,7 @@ public:
             Win32AppContext::windows[handle] = this;
     }
 
-    ~Win32PlatformWindow()
-    {
-        if (handle)
-        {
-            Win32AppContext::windows.Remove(handle);
-        }
-        DestroyWindow(handle);
-    }
+    ~Win32PlatformWindow() { close(); }
 
     virtual void setClientSize(uint32_t width, uint32_t height) override
     {
@@ -401,7 +396,15 @@ public:
         MoveWindow(handle, left, top, width, height, FALSE);
     }
 
-    virtual void close() override {}
+    virtual void close() override
+    {
+        if (handle)
+        {
+            Win32AppContext::windows.Remove(handle);
+        }
+        DestroyWindow(handle);
+        handle = NULL;
+    }
     virtual bool getFocused() override { return GetFocus() == handle; }
     virtual bool getVisible() override { return visible; }
     virtual WindowHandle getNativeHandle() override