Bump godot-cpp to beta8, libdatachannel to v0.18.0

libdatachannel and libjuice are now released under MPL 2.0.

Dependencies has been refactored under a `thirdparty` folder similar to
what we have in Godot, with a dedicated `thirdparty/README.md`
containing details information on dependencies upstreams, versions, and
licenses.

thirdparty/README.md

@@ -0,0 +1,82 @@
+# Third party libraries
+
+Please keep categories (`##` level) listed alphabetically and matching their
+respective folder names. Use two empty lines to separate categories for
+readability.
+
+
+## json
+
+- Upstream: https://github.com/nlohmann/json
+- Version: 3.10.5 (4f8fba14066156b73f1189a2b8bd568bde5284c5, 2022)
+- License: MIT
+
+Module location:
+
+- thirdparty/libdatachannel/deps/json
+
+
+## libdatachannel
+
+- Upstream: https://github.com/paullouisageneau/libdatachannel
+- Version: 0.18.0 (084445012d6c63c9f2cc250d88df553aed2eb189, 2022)
+- License: MPL 2.0
+
+Module location:
+
+- thirdparty/libdatachannel
+
+
+# libjuice
+
+- Upstream: https://github.com/paullouisageneau/libjuice
+- Version: 1.1.0 (0dabc046cd23da6908749e4c6add834ec29a7c49, 2022)
+- License: MPL 2.0
+
+Module location:
+
+- thirdparty/libdatachannel/deps/libjuice
+
+
+## libsrtp
+
+- Upstream: https://github.com/cisco/libsrtp
+- Version: 2.4.2 (90d05bf8980d16e4ac3f16c19b77e296c4bc207b, 2021)
+- License: BSD-3-Clause
+
+Module location:
+
+- thirdparty/libdatachannel/deps/libsrtp
+
+
+## openssl
+
+- Upstream: git://git.openssl.org/openssl.git
+- Version: 3.0.7 (19cc035b6c6f2283573d29c7ea7f7d675cf750ce, 2022)
+- License: Apache 2.0
+
+Module location:
+
+- thirdparty/openssl
+
+
+## plog
+
+- Upstream: https://github.com/SergiusTheBest/plog
+- Version: git (d8461e9d473e59fbcc1f79eee021550dcf81e618, 2021)
+- License: MPL 2.0
+
+Module location:
+
+- thirdparty/libdatachannel/deps/plog
+
+
+## usrsctp
+
+- Upstream: https://github.com/sctplab/usrsctp
+- Version: git (7c31bd35c79ba67084ce029511193a19ceb97447, 2021)
+- License: BSD-3-Clause
+
+Module location:
+
+- thirdparty/libdatachannel/deps/usrsctp