Lay the groundwork for collaborating on assistant panel (#13991)

This pull request introduces collaboration for the assistant panel by
turning `Context` into a CRDT. `ContextStore` is responsible for sending
and applying operations, as well as synchronizing missed changes while
the connection was lost.

Contexts are shared on a per-project basis, and only the host can share
them for now. Shared contexts can be accessed via the `History` tab in
the assistant panel.

<img width="1819" alt="image"
src="https://github.com/zed-industries/zed/assets/482957/c7ae46d2-cde3-4b03-b74a-6e9b1555c154">


Please note that this doesn't implement following yet, which is
scheduled for a subsequent pull request.

Release Notes:

- N/A

crates/assistant/Cargo.toml

@@ -12,6 +12,14 @@ workspace = true
 path = "src/assistant.rs"
 doctest = false
 
+[features]
+test-support = [
+    "editor/test-support",
+    "language/test-support",
+    "project/test-support",
+    "text/test-support",
+]
+
 [dependencies]
 anthropic = { workspace = true, features = ["schemars"] }
 anyhow.workspace = true
@@ -21,6 +29,7 @@ breadcrumbs.workspace = true
 cargo_toml.workspace = true
 chrono.workspace = true
 client.workspace = true
+clock.workspace = true
 collections.workspace = true
 command_palette_hooks.workspace = true
 editor.workspace = true
@@ -72,7 +81,9 @@ picker.workspace = true
 ctor.workspace = true
 editor = { workspace = true, features = ["test-support"] }
 env_logger.workspace = true
+language = { workspace = true, features = ["test-support"] }
 log.workspace = true
 project = { workspace = true, features = ["test-support"] }
 rand.workspace = true
+text = { workspace = true, features = ["test-support"] }
 unindent.workspace = true