feat(gx): sync index buffer in d3d backend

src/gx/d3d/CGxDeviceD3d.cpp

@@ -950,7 +950,18 @@ void CGxDeviceD3d::IStateSyncEnables() {
 }
 
 void CGxDeviceD3d::IStateSyncIndexPtr() {
-    // TODO
+    if (!this->m_primIndexDirty) {
+        return;
+    }
+
+    this->m_primIndexDirty = 0;
+
+    auto d3dIndexBuf = static_cast<LPDIRECT3DINDEXBUFFER9>(this->m_primIndexBuf->m_pool->m_apiSpecific);
+
+    if (this->m_d3dCurrentIndexBuf != d3dIndexBuf) {
+        this->m_d3dDevice->SetIndices(d3dIndexBuf);
+        this->m_d3dCurrentIndexBuf = d3dIndexBuf;
+    }
 }
 
 void CGxDeviceD3d::IStateSyncVertexPtrs() {

src/gx/d3d/CGxDeviceD3d.hpp

@@ -220,6 +220,7 @@ class CGxDeviceD3d : public CGxDevice {
     int32_t m_d3dIsHwDevice = 0;
     D3DDISPLAYMODE m_desktopDisplayMode;
     D3DFORMAT m_devAdapterFormat;
+    LPDIRECT3DINDEXBUFFER9 m_d3dCurrentIndexBuf;
     uint32_t m_deviceStates[DeviceStates_Last];
 
     // Virtual member functions