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FLASHING.md says how to take a newer version of the colleague's tree (copy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/geodesy/geographiclib.cpp

@@ -0,0 +1,43 @@
+#include <vanetza/geodesy/geographiclib.hpp>
+#include <GeographicLib/Geocentric.hpp>
+#include <GeographicLib/Geodesic.hpp>
+#include <GeographicLib/LocalCartesian.hpp>
+#include <limits>
+
+namespace vanetza
+{
+namespace geodesy
+{
+namespace geographiclib
+{
+
+units::Length distance(const GeodeticPosition& a, const GeodeticPosition& b)
+{
+    const auto& geod = GeographicLib::Geodesic::WGS84();
+    double distance_m = 0.0;
+    geod.Inverse(a.latitude / units::degree, a.longitude / units::degree,
+            b.latitude / units::degree, b.longitude / units::degree,
+            distance_m);
+    return (distance_m >= 0.0 ? distance_m : std::numeric_limits<double>::quiet_NaN()) * units::si::meter;
+}
+
+CartesianPosition local_cartesian(
+        const GeodeticPosition& origin,
+        const GeodeticPosition& position)
+{
+    const auto& earth = GeographicLib::Geocentric::WGS84();
+    GeographicLib::LocalCartesian proj {
+            origin.latitude / units::degree,
+            origin.longitude / units::degree,
+            0.0, earth
+    };
+    double result_x, result_y, unused_z = 0.0;
+    proj.Forward(position.latitude / units::degree,
+            position.longitude / units::degree, 0.0,
+            result_x, result_y, unused_z);
+    return CartesianPosition(result_x * units::si::meter, result_y * units::si::meter);
+}
+
+} // namespace geographiclib
+} // namespace geodesy
+} // namespace vanetza