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/multi_buffer/Cargo.toml

@@ -35,6 +35,7 @@ log.workspace = true
 parking_lot.workspace = true
 rand.workspace = true
 settings.workspace = true
+serde.workspace = true
 smallvec.workspace = true
 sum_tree.workspace = true
 text.workspace = true