channel projects (#8456)

Add plumbing for hosted projects. This will currently show them if they
exist
but provides no UX to create/rename/delete them.

Also changed the `ChannelId` type to not auto-cast to u64; this avoids
type
confusion if you have multiple id types.


Release Notes:

- N/A

crates/collab/src/tests/random_channel_buffer_tests.rs

@@ -253,7 +253,7 @@ impl RandomizedTest for RandomChannelBufferTest {
                         .channel_buffers()
                         .deref()
                         .iter()
-                        .find(|b| b.read(cx).channel_id == channel_id.to_proto())
+                        .find(|b| b.read(cx).channel_id.0 == channel_id.to_proto())
                     {
                         let channel_buffer = channel_buffer.read(cx);