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/collab/Cargo.toml

@@ -90,6 +90,7 @@ language = { workspace = true, features = ["test-support"] }
 live_kit_client = { workspace = true, features = ["test-support"] }
 lsp = { workspace = true, features = ["test-support"] }
 menu.workspace = true
+multi_buffer = { workspace = true, features = ["test-support"] }
 node_runtime.workspace = true
 notifications = { workspace = true, features = ["test-support"] }
 pretty_assertions.workspace = true