feat: initialize Y.Docs from VSC buffers

[Vtec234]

This PR changes how Y.Docs are initialized in collab-server when they are opened for the first time. Previously, collab-server would open the given file on disk and read its contents. In this PR, VSC instead sends the contents of its text buffer to collab-server when YTextBinding is constructed. This produces a different outcome in case the VSC buffer has unsaved changes. Previously, they would be discarded, whereas now they are kept.

Addresses, but does not entirely fix, #146 - renaming once works now, but renaming back to an old name will restore the last buffer state of the old name.

This is moving in the direction of having collab-server sync only the open text buffers, but not the project files: disk IO is now the sole purview of VSC clients. After this PR, collab-server will not even have access to project files.

Instrumentally, we introduce a tRPC connection between VSC and collab-server to communicate events that Hocuspocus/Yjs doesn't handle natively.

[robsimmons]

Thanks for revising this to do a bit less. The tRPC communication channel is likely to be helpful for other things, and with the exception of increasing the delay before initFromRemote overwrites the buffer, this pretty clearly improves things more than it breaks them without adding a lot of cruft.

Please file and/or link an issue about the initFromRemote problem if there isn't one before you merge.