Keep the colleague's microbu-esp32c5 tree in this repository

obu-firmware builds against vanetza-idf from microbu-esp32c5/external, but
that tree was gitignored, so a clone of this repository could not build the
firmware it ships. It is now committed here as ordinary files in its own
folder, microbu-esp32c5/: the colleague's commit cf4b99f plus the V2X2MAP
bridge's signature verification (--trust) used on the bench. Nothing is
fetched from or pushed to the colleague's repository; this repository and
its remotes carry everything. The folder's own .gitignore keeps build output,
downloaded components and private key material out, as it did there; the
committed file set is identical to that repository's tracked files.

The ESP32-C5 is still flashed from obu-firmware/, which only takes
vanetza-idf from microbu-esp32c5/, so the two stay separate folders.
FLASHING.md says how to take a newer version of the colleague's tree (copy
it over the folder, rebuild, test, commit).

microbu-esp32c5/external/vanetza-idf/vanetza/geonet/gbc_gac_header.cpp

@@ -0,0 +1,129 @@
+#include "gbc_gac_header.hpp"
+#include "areas.hpp"
+#include <cmath>
+
+namespace vanetza
+{
+namespace geonet
+{
+namespace detail
+{
+
+class set_distance_visitor : public boost::static_visitor<>
+{
+public:
+    set_distance_visitor(GbcGacHeader& hdr) : m_header(hdr) {}
+
+    void operator()(const Circle& circle)
+    {
+        m_header.distance_a = circle.r;
+        m_header.distance_b = 0;
+    }
+
+    void operator()(const Rectangle& rect)
+    {
+        m_header.distance_a = rect.a;
+        m_header.distance_b = rect.b;
+    }
+
+    void operator()(const Ellipse& elip)
+    {
+        m_header.distance_a = elip.a;
+        m_header.distance_b = elip.b;
+    }
+
+private:
+    GbcGacHeader& m_header;
+};
+
+class get_distance_visitor : public boost::static_visitor<>
+{
+public:
+    get_distance_visitor(const GbcGacHeader& hdr) : m_header(hdr) {}
+
+    void operator()(Circle& circle)
+    {
+        circle.r = m_header.distance_a;
+    }
+
+    void operator()(Rectangle& rect)
+    {
+        rect.a = m_header.distance_a;
+        rect.b = m_header.distance_b;
+    }
+
+    void operator()(Ellipse& elip)
+    {
+        elip.a = m_header.distance_a;
+        elip.b = m_header.distance_b;
+    }
+
+private:
+    const GbcGacHeader& m_header;
+};
+
+constexpr std::size_t GbcGacHeader::length_bytes;
+
+void GbcGacHeader::destination(const Area& area)
+{
+    this->position(area.position);
+    angle = static_cast<angle_u16t>(area.angle);
+    set_distance_visitor visitor(*this);
+    boost::apply_visitor(visitor, area.shape);
+}
+
+Area GbcGacHeader::destination(const decltype(Area::shape)& shape) const
+{
+    Area area;
+    area.shape = shape;
+    area.position = this->position();
+    area.angle = static_cast<units::Angle>(angle);
+    get_distance_visitor visitor(*this);
+    boost::apply_visitor(visitor, area.shape);
+    return area;
+}
+
+void GbcGacHeader::position(const GeodeticPosition& position)
+{
+    geo_area_pos_latitude = geo_angle_i32t::from_value(std::round(position.latitude.value() * 1e7));
+    geo_area_pos_longitude = geo_angle_i32t::from_value(std::round(position.longitude.value() * 1e7));
+}
+
+GeodeticPosition GbcGacHeader::position() const
+{
+    return GeodeticPosition(
+            static_cast<units::GeoAngle>(geo_area_pos_latitude),
+            static_cast<units::GeoAngle>(geo_area_pos_longitude)
+        );
+}
+
+void serialize(const GbcGacHeader& header, OutputArchive& ar)
+{
+    geonet::serialize(header.sequence_number, ar);
+    geonet::serialize(host_cast(header.reserved1), ar);
+    geonet::serialize(header.source_position, ar);
+    geonet::serialize(header.geo_area_pos_latitude, ar);
+    geonet::serialize(header.geo_area_pos_longitude, ar);
+    geonet::serialize(header.distance_a, ar);
+    geonet::serialize(header.distance_b, ar);
+    geonet::serialize(header.angle, ar);
+    geonet::serialize(host_cast(header.reserved2), ar);
+}
+
+void deserialize(GbcGacHeader& header, InputArchive& ar)
+{
+    geonet::deserialize(header.sequence_number, ar);
+    geonet::deserialize(header.reserved1, ar);
+    geonet::deserialize(header.source_position, ar);
+    geonet::deserialize(header.geo_area_pos_latitude, ar);
+    geonet::deserialize(header.geo_area_pos_longitude, ar);
+    geonet::deserialize(header.distance_a, ar);
+    geonet::deserialize(header.distance_b, ar);
+    geonet::deserialize(header.angle, ar);
+    geonet::deserialize(header.reserved2, ar);
+}
+
+} // namespace detail
+} // namespace geonet
+} // namepsace vanetza
+