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/client/src/user.rs

@@ -46,11 +46,6 @@ impl ProjectId {
     }
 }
 
-#[derive(
-    Debug, PartialEq, Eq, PartialOrd, Ord, Hash, Clone, Copy, serde::Serialize, serde::Deserialize,
-)]
-pub struct DevServerProjectId(pub u64);
-
 #[derive(Debug, Clone, Copy, PartialEq, Eq)]
 pub struct ParticipantIndex(pub u32);