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FLASHING.md says how to take a newer version of the colleague's tree (copy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/asn1/support/xer_encoder.h

@@ -0,0 +1,83 @@
+/*-
+ * Copyright (c) 2004-2017 Lev Walkin <vlm@lionet.info>. All rights reserved.
+ * Redistribution and modifications are permitted subject to BSD license.
+ */
+#ifndef	_XER_ENCODER_H_
+#define	_XER_ENCODER_H_
+
+#include "asn_application.h"
+
+#ifdef __cplusplus
+extern "C" {
+#endif
+
+struct asn_TYPE_descriptor_s;	/* Forward declaration */
+
+/* Flags used by the xer_encode() and (*xer_type_encoder_f), defined below */
+enum xer_encoder_flags_e {
+	/* Mode of encoding */
+	XER_F_BASIC	= 0x01,	/* BASIC-XER (pretty-printing) */
+	XER_F_CANONICAL	= 0x02	/* Canonical XER (strict rules) */
+};
+
+/*
+ * The XER encoder of any type. May be invoked by the application.
+ * Produces CANONICAL-XER and BASIC-XER depending on the (xer_flags).
+ */
+asn_enc_rval_t xer_encode(const struct asn_TYPE_descriptor_s *type_descriptor,
+                          const void *struct_ptr, /* Structure to be encoded */
+                          enum xer_encoder_flags_e xer_flags,
+                          asn_app_consume_bytes_f *consume_bytes_cb,
+                          void *app_key /* Arbitrary callback argument */
+);
+
+/*
+ * The variant of the above function which dumps the BASIC-XER (XER_F_BASIC)
+ * output into the chosen file pointer.
+ * RETURN VALUES:
+ * 	 0: The structure is printed.
+ * 	-1: Problem printing the structure.
+ * WARNING: No sensible errno value is returned.
+ */
+int xer_fprint(FILE *stream, const struct asn_TYPE_descriptor_s *td,
+               const void *struct_ptr);
+
+/*
+ * A helper function that uses XER encoding/decoding to verify that:
+ * - Both structures encode into the same BASIC XER.
+ * - Both resulting XER byte streams can be decoded back.
+ * - Both decoded structures encode into the same BASIC XER (round-trip).
+ * All of this verifies equivalence between structures and a round-trip.
+ * ARGUMENTS:
+ *  (opt_debug_stream)  - If specified, prints ongoing details.
+ */
+enum xer_equivalence_e {
+    XEQ_SUCCESS,          /* The only completely positive return value */
+    XEQ_FAILURE,          /* General failure */
+    XEQ_ENCODE1_FAILED,   /* First structure XER encoding failed */
+    XEQ_ENCODE2_FAILED,   /* Second structure XER encoding failed */
+    XEQ_DIFFERENT,        /* Structures encoded into different XER */
+    XEQ_DECODE_FAILED,    /* Decode of the XER data failed */
+    XEQ_ROUND_TRIP_FAILED /* Bad round-trip */
+};
+enum xer_equivalence_e xer_equivalent(
+    const struct asn_TYPE_descriptor_s *type_descriptor, const void *struct1,
+    const void *struct2, FILE *opt_debug_stream);
+
+/*
+ * Type of the generic XER encoder.
+ */
+typedef asn_enc_rval_t(xer_type_encoder_f)(
+    const struct asn_TYPE_descriptor_s *type_descriptor,
+    const void *struct_ptr, /* Structure to be encoded */
+    int ilevel,             /* Level of indentation */
+    enum xer_encoder_flags_e xer_flags,
+    asn_app_consume_bytes_f *consume_bytes_cb, /* Callback */
+    void *app_key                              /* Arbitrary callback argument */
+);
+
+#ifdef __cplusplus
+}
+#endif
+
+#endif	/* _XER_ENCODER_H_ */