overlay: implement dx11 backend (#707)

## Link to GitHub Issue or related Pull Request, if one exists
Fixes #134 

## Description of change
Add ImGui DX11 backend implementation, and integrate into the spice
overlay.

The tricky part is that some of the Unity games:

1. Launch multiple windows, and
2. Can be resized (even full screen games launch at a certain resolution
and then expand to fit desktop resolution)
3. lazy load DX11 DLLs

This PR also adds screenshot functionality, but screen resize is not
implemented.

## Testing

Seems to be working for most games. Need to do final tests for:

- [x] CCJ (attract movie plays as well)
- [x] Busou Shinki (title movie plays)
- [x] MFG
- [x] QuizKnock
- [x] Polaris Chord
- [x] check dx9 for regression

src/spice2x/hooks/graphics/backends/d3d11/d3d11_factory.cpp

@@ -0,0 +1,102 @@
+// dx11 factory vtable hooks. patches CreateSwapChain / CreateSwapChainForHwnd
+// so we can install_swapchain_hooks against every newly-created swapchain.
+
+#include "d3d11_backend.h"
+
+#ifdef SPICE_D3D11
+
+#include <mutex>
+
+#include <windows.h>
+#include <d3d11.h>
+#include <dxgi.h>
+#include <dxgi1_2.h>
+
+#include "d3d11_internal.h"
+
+namespace {
+
+using CreateSwapChain_t = HRESULT(STDMETHODCALLTYPE *)(
+    IDXGIFactory *, IUnknown *, DXGI_SWAP_CHAIN_DESC *, IDXGISwapChain **);
+using CreateSwapChainForHwnd_t = HRESULT(STDMETHODCALLTYPE *)(
+    IDXGIFactory2 *, IUnknown *, HWND,
+    const DXGI_SWAP_CHAIN_DESC1 *,
+    const DXGI_SWAP_CHAIN_FULLSCREEN_DESC *,
+    IDXGIOutput *, IDXGISwapChain1 **);
+
+CreateSwapChain_t CreateSwapChain_orig = nullptr;
+CreateSwapChainForHwnd_t CreateSwapChainForHwnd_orig = nullptr;
+
+bool g_factory_hooked = false;
+bool g_factory2_hooked = false;
+std::mutex g_hook_mutex;
+
+HRESULT STDMETHODCALLTYPE CreateSwapChain_hook(
+        IDXGIFactory *factory, IUnknown *pDevice,
+        DXGI_SWAP_CHAIN_DESC *pDesc, IDXGISwapChain **ppSwapChain)
+{
+    HRESULT res = CreateSwapChain_orig(factory, pDevice, pDesc, ppSwapChain);
+    if (SUCCEEDED(res) && ppSwapChain && *ppSwapChain) {
+        if (pDesc) {
+            d3d11_hooks::note_main_hwnd(pDesc->OutputWindow);
+        }
+        d3d11_hooks::install_swapchain_hooks(*ppSwapChain);
+    }
+    return res;
+}
+
+HRESULT STDMETHODCALLTYPE CreateSwapChainForHwnd_hook(
+        IDXGIFactory2 *factory, IUnknown *pDevice, HWND hWnd,
+        const DXGI_SWAP_CHAIN_DESC1 *pDesc,
+        const DXGI_SWAP_CHAIN_FULLSCREEN_DESC *pFullscreenDesc,
+        IDXGIOutput *pRestrictToOutput, IDXGISwapChain1 **ppSwapChain)
+{
+    HRESULT res = CreateSwapChainForHwnd_orig(
+        factory, pDevice, hWnd, pDesc, pFullscreenDesc, pRestrictToOutput, ppSwapChain);
+    if (SUCCEEDED(res) && ppSwapChain && *ppSwapChain) {
+        d3d11_hooks::note_main_hwnd(hWnd);
+        d3d11_hooks::install_swapchain_hooks(*ppSwapChain);
+    }
+    return res;
+}
+
+// QI-and-hook helper: dedupes the IDXGIFactory / IDXGIFactory2 install paths.
+template<typename Iface>
+void install_on(IUnknown *factory, bool &flag,
+                size_t vtbl_index, void *hook, void **orig, const char *name)
+{
+    if (flag) {
+        return;
+    }
+    Iface *f = nullptr;
+    if (FAILED(factory->QueryInterface(IID_PPV_ARGS(&f))) || !f) {
+        return;
+    }
+    if (d3d11_hooks::hook_vtbl(f, vtbl_index, hook, orig, name)) {
+        flag = true;
+    }
+    f->Release();
+}
+
+} // namespace
+
+namespace d3d11_hooks {
+
+void install_factory_hooks(IUnknown *factory) {
+    if (!factory) {
+        return;
+    }
+    std::lock_guard<std::mutex> lock(g_hook_mutex);
+
+    install_on<IDXGIFactory>(factory, g_factory_hooked, 10,
+        (void *) CreateSwapChain_hook, (void **) &CreateSwapChain_orig,
+        "IDXGIFactory::CreateSwapChain");
+
+    install_on<IDXGIFactory2>(factory, g_factory2_hooked, 15,
+        (void *) CreateSwapChainForHwnd_hook, (void **) &CreateSwapChainForHwnd_orig,
+        "IDXGIFactory2::CreateSwapChainForHwnd");
+}
+
+}
+
+#endif // SPICE_D3D11