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FLASHING.md says how to take a newer version of the colleague's tree (copy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/security/v3/distance.cpp

@@ -0,0 +1,53 @@
+#include <vanetza/common/position_fix.hpp>
+#include <vanetza/asn1/security_profile.hpp>
+#include VANETZA_ASN1_SECURITY_HEADER(Latitude.h)
+#include VANETZA_ASN1_SECURITY_HEADER(Longitude.h)
+#include VANETZA_ASN1_SECURITY_HEADER(TwoDLocation.h)
+#include <vanetza/security/v3/distance.hpp>
+#include <boost/units/cmath.hpp>
+
+namespace vanetza
+{
+namespace security
+{
+namespace v3
+{
+
+units::Length distance(const PositionFix& one, const asn1::TwoDLocation& other)
+{
+    static const auto earth_radius = 6371000.0 * units::si::meter;
+    const auto other_lat = convert_latitude(other.latitude);
+    const auto other_lon = convert_longitude(other.longitude);
+    const units::Angle delta_phi { one.latitude - other_lat };
+    const units::Angle delta_lambda { one.longitude - other_lon };
+    const auto sin_delta_phi = sin(delta_phi / 2.0);
+    const auto sin_delta_lambda = sin(delta_lambda / 2.0);
+    const auto a = sin_delta_phi * sin_delta_phi +
+        cos(one.latitude) * cos(other_lat) * sin_delta_lambda * sin_delta_lambda;
+    const auto c = 2.0 * atan2(sqrt(a), sqrt(1 - a));
+    return earth_radius * c;
+}
+
+units::GeoAngle convert_latitude(const asn1::Latitude& in)
+{
+    static constexpr long latitude_scale = Vanetza_Security_NinetyDegreeInt_max;
+    if (in >= Vanetza_Security_NinetyDegreeInt_min && in <= Vanetza_Security_NinetyDegreeInt_max) {
+        return in * 90.0 / latitude_scale * units::degree;
+    } else {
+        return units::GeoAngle::from_value(std::numeric_limits<double>::quiet_NaN());
+    }
+}
+
+units::GeoAngle convert_longitude(const asn1::Longitude& in)
+{
+    static constexpr long longitude_scale = Vanetza_Security_OneEightyDegreeInt_max;
+    if (in >= Vanetza_Security_OneEightyDegreeInt_min && in <= Vanetza_Security_OneEightyDegreeInt_max) {
+        return in * 180.0 / longitude_scale * units::degree;
+    } else {
+        return units::GeoAngle::from_value(std::numeric_limits<double>::quiet_NaN());
+    }
+}
+
+} // namespace v3
+} // namespace security
+} // namespace vanetza