Cpp api for getting usd context

Omniverse Core Platform Extensions
5

In case anyone needs to get the stage

#include <pxr/usd/usd/stage.h>
#include <pxr/usd/usdUtils/stageCache.h>
#include <usdrt/scenegraph/usd/usd/stage.h>

static usdrt::UsdStageRefPtr getActiveStage()
    {
        const std::vector<PXR_NS::UsdStageRefPtr> allStages = PXR_NS::UsdUtilsStageCache::Get().GetAllStages();
        if (allStages.size() != 1) // only support one USD stage
            return nullptr;

        auto stage_id = PXR_NS::UsdUtilsStageCache::Get().GetId(allStages[0]).ToLongInt();
        return usdrt::UsdStage::Attach(omni::fabric::UsdStageId(stage_id));
    }