Restructure persistence of remote workspaces to make room for WSL and other non-ssh remote projects (#36714)

This is another pure refactor, to prepare for adding direct WSL support.

###  Todo

* [x] Represent `paths` in the same way for all workspaces, instead of
having a completely separate SSH representation
* [x] Adjust sqlite tables
    * [x] `ssh_projects` -> `ssh_connections` (drop paths)
    * [x] `workspaces.local_paths` -> `paths`
    * [x] remove duplicate path columns on `workspaces`
* [x] Add migrations for backward-compatibility

Release Notes:

- N/A

---------

Co-authored-by: Mikayla Maki <mikayla.c.maki@gmail.com>

crates/workspace/Cargo.toml

@@ -29,7 +29,6 @@ test-support = [
 any_vec.workspace = true
 anyhow.workspace = true
 async-recursion.workspace = true
-bincode.workspace = true
 call.workspace = true
 client.workspace = true
 clock.workspace = true
@@ -80,5 +79,6 @@ project = { workspace = true, features = ["test-support"] }
 session = { workspace = true, features = ["test-support"] }
 settings = { workspace = true, features = ["test-support"] }
 http_client = { workspace = true, features = ["test-support"] }
+pretty_assertions.workspace = true
 tempfile.workspace = true
 zlog.workspace = true