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FLASHING.md says how to take a newer version of the colleague's tree (copy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

@@ -0,0 +1,95 @@
+#include <vanetza/geonet/variant_pdu.hpp>
+#include <boost/variant/static_visitor.hpp>
+
+namespace vanetza
+{
+namespace geonet
+{
+
+VariantPdu::VariantPdu(const Pdu& pdu) :
+    m_basic(pdu.basic()), m_common(pdu.common()), m_extended(pdu.extended_variant()),
+    m_secured(pdu.secured() ? boost::make_optional(*pdu.secured()) : boost::none)
+{
+}
+
+VariantPdu::VariantPdu(const VariantPdu& pdu) :
+    VariantPdu(static_cast<const Pdu&>(pdu))
+{
+}
+
+VariantPdu& VariantPdu::operator=(const VariantPdu& pdu)
+{
+    return operator=(static_cast<const Pdu&>(pdu));
+}
+
+VariantPdu& VariantPdu::operator=(const Pdu& pdu)
+{
+    m_basic = pdu.basic();
+    m_common = pdu.common();
+    m_extended = pdu.extended_variant();
+    if (pdu.secured()) {
+        m_secured = *pdu.secured();
+    } else {
+        m_secured = boost::none;
+    }
+
+    return *this;
+}
+
+BasicHeader& VariantPdu::basic()
+{
+    return m_basic;
+}
+
+const BasicHeader& VariantPdu::basic() const
+{
+    return m_basic;
+}
+
+CommonHeader& VariantPdu::common()
+{
+    return m_common;
+}
+
+const CommonHeader& VariantPdu::common() const
+{
+    return m_common;
+}
+
+HeaderVariant& VariantPdu::extended_variant()
+{
+    return m_extended;
+}
+
+HeaderConstRefVariant VariantPdu::extended_variant() const
+{
+    return m_extended;
+}
+
+VariantPdu::SecuredMessage* VariantPdu::secured()
+{
+    return m_secured.get_ptr();
+}
+
+const VariantPdu::SecuredMessage* VariantPdu::secured() const
+{
+    return m_secured.get_ptr();
+}
+
+void VariantPdu::secured(const SecuredMessage& smsg)
+{
+    m_secured = smsg;
+}
+
+void VariantPdu::secured(SecuredMessage&& smsg)
+{
+    m_secured.emplace(std::move(smsg));
+}
+
+std::unique_ptr<Pdu> VariantPdu::clone() const
+{
+    return std::unique_ptr<Pdu> { new VariantPdu(*this) };
+}
+
+} // namespace geonet
+} // namespace vanetza