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FLASHING.md says how to take a newer version of the colleague's tree (copy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/ecc_point.hpp

@@ -0,0 +1,83 @@
+#ifndef CFE4DC34_AD31_47E8_9EB2_1B98C6FB0887
+#define CFE4DC34_AD31_47E8_9EB2_1B98C6FB0887
+
+#include <vanetza/common/byte_buffer.hpp>
+#include <boost/variant/variant.hpp>
+
+namespace vanetza
+{
+namespace security
+{
+
+// forward declarations
+struct PublicKey;
+namespace ecdsa256 { struct PublicKey; }
+
+/// X_Coordinate_Only specified in TS 103 097 v1.2.1 in section 4.2.5
+struct X_Coordinate_Only
+{
+    ByteBuffer x;
+};
+
+/// Compressed_Lsb_Y_0 specified in TS 103 097 v1.2.1 in section 4.2.5
+struct Compressed_Lsb_Y_0
+{
+    ByteBuffer x;
+};
+
+/// Compressed_Lsb_Y_1 specified in TS 103 097 v1.2.1 in section 4.2.5
+struct Compressed_Lsb_Y_1
+{
+    ByteBuffer x;
+};
+
+/// Uncompressed specified in TS 103 097 v1.2.1 in section 4.2.5
+struct Uncompressed
+{
+    ByteBuffer x;
+    ByteBuffer y;
+};
+
+/// EccPoint specified in TS 103 097 v1.2.1 in section 4.2.5
+using EccPoint = boost::variant<
+    X_Coordinate_Only,
+    Compressed_Lsb_Y_0,
+    Compressed_Lsb_Y_1,
+    Uncompressed
+>;
+
+/**
+ * \brief calculate byte length of ECC point structure
+ * \param ecc_point 
+ * \return length in bytes
+ */
+std::size_t get_length(const EccPoint& ecc_point);
+
+/**
+ * \brief Convert EccPoint for signature calculation
+ * Uses ecc_point.x as relevant field for signatures.
+ *
+ * \param ecc_point
+ * \return binary representation of ECC point
+ */
+ByteBuffer convert_for_signing(const EccPoint& ecc_point);
+
+/**
+ * \brief Convert a public key into an ECC point, preserving its compression
+ * \param public_key public key (uncompressed or compressed)
+ * \return ECC point matching the key's own point format
+ */
+EccPoint make_ecc_point(const PublicKey& public_key);
+
+/**
+ * \brief Compressed ECC point from public key
+ * \param public_key
+ * \return compressed ECC point
+ */
+EccPoint compress_public_key(const PublicKey& public_key);
+EccPoint compress_public_key(const ecdsa256::PublicKey& public_key);
+
+} // namespace security
+} // namespace vanetza
+
+#endif /* CFE4DC34_AD31_47E8_9EB2_1B98C6FB0887 */