Introduce DisplayRow, MultiBufferRow newtypes and BufferRow type alias (#11656)

Part of https://github.com/zed-industries/zed/issues/8081

To avoid confusion and bugs when converting between various row `u32`'s,
use different types for each.
Further PRs should split `Point` into buffer and multi buffer variants
and make the code more readable.

Release Notes:

- N/A

---------

Co-authored-by: Piotr <piotr@zed.dev>

crates/vim/Cargo.toml

@@ -26,6 +26,7 @@ gpui.workspace = true
 itertools.workspace = true
 language.workspace = true
 log.workspace = true
+multi_buffer.workspace = true
 nvim-rs = { git = "https://github.com/KillTheMule/nvim-rs", branch = "master", features = [
     "use_tokio",
 ], optional = true }