MPL-covered dependency source for rdp-cli

These are the actual libdatachannel and libjuice source trees used by
the build, including rdp-cli's libdatachannel RTCP clock modification.
Their original LICENSE files and source copyright notices are retained.
The included DependencyLock.cmake identifies upstream revisions and
source archive hashes; PatchLibDataChannel.cmake describes the change.
Other build dependencies are not included here; their pinned archive
URLs and hashes are in that lock file. No compiled runtime is included.

Distributors: make this source archive available to recipients of the
corresponding executable, and tell them how to obtain it. It is source
material, not a runtime dependency, and need not sit beside the EXE.
