ipa: Switch to the plain C API

Switch IPA communication to the plain C API. As the IPAInterface class
is easier to use for pipeline handlers than a plain C API, retain it and
add an IPAContextWrapper that translate between the C++ and the C APIs.

On the IPA module side usage of IPAInterface may be desired for IPAs
implemented in C++ that want to link to libcamera. For those IPAs, a new
IPAInterfaceWrapper helper class is introduced to wrap the IPAInterface
implemented internally by the IPA module into an ipa_context,
ipa_context_ops and ipa_callback_ops.

Signed-off-by: Jacopo Mondi <jacopo@jmondi.org>
Signed-off-by: Laurent Pinchart <laurent.pinchart@ideasonboard.com>
Reviewed-by: Niklas Söderlund <niklas.soderlund@ragnatech.se>

src/libcamera/proxy/worker/ipa_proxy_linux_worker.cpp

@@ -72,9 +72,9 @@ int main(int argc, char **argv)
 	}
 	socket.readyRead.connect(&readyRead);
 
-	std::unique_ptr<IPAInterface> ipa = ipam->createInstance();
-	if (!ipa) {
-		LOG(IPAProxyLinuxWorker, Error) << "Failed to create IPA interface";
+	struct ipa_context *ipac = ipam->createContext();
+	if (!ipac) {
+		LOG(IPAProxyLinuxWorker, Error) << "Failed to create IPA context";
 		return EXIT_FAILURE;
 	}
 
@@ -85,5 +85,7 @@ int main(int argc, char **argv)
 	while (1)
 		dispatcher->processEvents();
 
+	ipac->ops->destroy(ipac);
+
 	return 0;
 }