NodeJS bindings: Support for MSC3983

[turt2live]

(relative priority: low, as of writing)

MSC: matrix-org/matrix-spec-proposals#3983
bot-sdk(NodeJS) implementation: turt2live/matrix-bot-sdk#307

I think to make MSC3983 work over the bindings, we'd need a way (function? flag?) to tell the OlmMachine that it shouldn't bother doing /key/upload for anything other than the fallback keys. Then, a function to route the /keys/claim query into the OlmMachine to have it do stuff.

Note that the implementation effort here is effectively to treat all OTKs as "uploaded" then manually track which ones are used in claim responses, followed by which ones are actually used in toDevice messages. The last bit (toDevice messages) is already present.