sdvx: implement NVAPI for non-NVIDIA GPUs (#816)

## Link to GitHub Issue or related Pull Request, if one exists
n/a

## Description of change

In summary: for SDVX VM mode, this PR eliminates the need for `Note FPS
Target 120Hz` / `Game FPS Target 120Hz` patches typically used for AMD
GPU via synthetic responses provided via a fake NVAPI layer.

Before this change, playing on AMD GPU required patches to force the
game to render at 60Hz (See #107 for relevant discussion). Basically, if
NVAPI query fails, the game shows

`I:NvDisplayConfig: GetMainDisplayRefreshRate = 60.000hz (DUMMY)`

the game renders at 120Hz but the notes render at 60Hz, which would look
stuttery.

After this change, even without a real `nvapi64.dll`, spice will provide
a stub implementation, just enough to convince the game that the main
display is 120Hz, which causes notes to render at 120Hz as well.

This can be overridden by `-graphics-force-refresh` option.

Important note: if user has the `Note FPS Target 60Hz` patch but running
the game at 120Hz, before this change the notes would render at 60Hz,
but after this they will be at 120Hz. I don't know why anyone would
intentionally lower the notes framerate, so this is not going to be
fixed. If the user wants to run the game at 60Hz they can do so via
`-graphics-force-refresh`.

Another change - `-nonvapi` will always force down this synthetic nvapi
path, even if the system has the real `nvapi64.dll`. Even on NVDIA GPU
this option can be used to force this.

## Testing

src/spice2x/hooks/graphics/nvapi_impl.h

@@ -0,0 +1,14 @@
+#pragma once
+
+#ifdef SPICE64
+
+#include <cstdint>
+#include <windows.h>
+
+namespace nvapi_impl {
+
+bool initialize(HINSTANCE dll, uint32_t main_refresh_hz, uint32_t sub_refresh_hz);
+
+}
+
+#endif