Convert .tgs with go libraries (and cgo) (telegram) (#1569)

This commit adds support for go/cgo tgs conversion when building with the -tags `cgo`
The default binaries are still "pure" go and uses the old way of converting.

* Move lottie_convert.py conversion code to its own file

* Add optional libtgsconverter

* Update vendor

* Apply suggestions from code review

* Update bridge/helper/libtgsconverter.go

Co-authored-by: Wim <wim@42.be>

vendor/github.com/Benau/go_rlottie/vector_vcowptr.h

@@ -0,0 +1,126 @@
+/*
+ * Copyright (c) 2020 Samsung Electronics Co., Ltd. All rights reserved.
+
+ * Permission is hereby granted, free of charge, to any person obtaining a copy
+ * of this software and associated documentation files (the "Software"), to deal
+ * in the Software without restriction, including without limitation the rights
+ * to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
+ * copies of the Software, and to permit persons to whom the Software is
+ * furnished to do so, subject to the following conditions:
+
+ * The above copyright notice and this permission notice shall be included in all
+ * copies or substantial portions of the Software.
+
+ * THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
+ * IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
+ * FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
+ * AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
+ * LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
+ * OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE
+ * SOFTWARE.
+ */
+
+#ifndef VCOWPTR_H
+#define VCOWPTR_H
+
+#include <cassert>
+#include <atomic>
+
+template <typename T>
+class vcow_ptr {
+    struct model {
+        std::atomic<std::size_t> mRef{1};
+
+        model() = default;
+
+        template <class... Args>
+        explicit model(Args&&... args) : mValue(std::forward<Args>(args)...){}
+        explicit model(const T& other) : mValue(other){}
+
+        T mValue;
+    };
+    model* mModel;
+
+public:
+    using element_type = T;
+
+    vcow_ptr()
+    {
+        static model default_s;
+        mModel = &default_s;
+        ++mModel->mRef;
+    }
+
+    ~vcow_ptr()
+    {
+        if (mModel && (--mModel->mRef == 0)) delete mModel;
+    }
+
+    template <class... Args>
+    explicit vcow_ptr(Args&&... args) : mModel(new model(std::forward<Args>(args)...))
+    {
+    }
+
+    vcow_ptr(const vcow_ptr& x) noexcept : mModel(x.mModel)
+    {
+        assert(mModel);
+        ++mModel->mRef;
+    }
+    vcow_ptr(vcow_ptr&& x) noexcept : mModel(x.mModel)
+    {
+        assert(mModel);
+        x.mModel = nullptr;
+    }
+
+    auto operator=(const vcow_ptr& x) noexcept -> vcow_ptr&
+    {
+        *this = vcow_ptr(x);
+        return *this;
+    }
+
+    auto operator=(vcow_ptr&& x) noexcept -> vcow_ptr&
+    {
+        auto tmp = std::move(x);
+        swap(*this, tmp);
+        return *this;
+    }
+
+    auto operator*() const noexcept -> const element_type& { return read(); }
+
+    auto operator-> () const noexcept -> const element_type* { return &read(); }
+
+    std::size_t refCount() const noexcept
+    {
+        assert(mModel);
+
+        return mModel->mRef;
+    }
+
+    bool unique() const noexcept
+    {
+        assert(mModel);
+
+        return mModel->mRef == 1;
+    }
+
+    auto write() -> element_type&
+    {
+        if (!unique()) *this = vcow_ptr(read());
+
+        return mModel->mValue;
+    }
+
+    auto read() const noexcept -> const element_type&
+    {
+        assert(mModel);
+
+        return mModel->mValue;
+    }
+
+    friend inline void swap(vcow_ptr& x, vcow_ptr& y) noexcept
+    {
+        std::swap(x.mModel, y.mModel);
+    }
+};
+
+#endif  // VCOWPTR_H