Move assets to their own crate, load keymaps in vim tests

Also, move assets folder to the top-level.

Co-authored-by: Keith Simmons <keith@zed.dev>

crates/vim/Cargo.toml

@@ -8,6 +8,7 @@ path = "src/vim.rs"
 doctest = false
 
 [dependencies]
+assets = { path = "../assets" }
 collections = { path = "../collections" }
 editor = { path = "../editor" }
 gpui = { path = "../gpui" }