sum_tree: Do not implement Dimension on tuples, use new Dimensions wrapper instead (#35482)

This is a bit of a readability improvement IMHO; I often find myself
confused when dealing when dimension pairs, as there's no easy way to
jump to the implementation of a dimension for tuples to remind myself
for the n-th time how exactly that impl works. Now it should be possible
to jump directly to that impl.

Another bonus is that Dimension supports 3-ary tuples as well - by using
a () as a default value of a 3rd dimension.


Release Notes:

- N/A

crates/project/src/lsp_store.rs

@@ -96,6 +96,7 @@ use std::{
     sync::Arc,
     time::{Duration, Instant},
 };
+use sum_tree::Dimensions;
 use text::{Anchor, BufferId, LineEnding, OffsetRangeExt};
 use url::Url;
 use util::{
@@ -7253,7 +7254,9 @@ impl LspStore {
 
             let build_incremental_change = || {
                 buffer
-                    .edits_since::<(PointUtf16, usize)>(previous_snapshot.snapshot.version())
+                    .edits_since::<Dimensions<PointUtf16, usize>>(
+                        previous_snapshot.snapshot.version(),
+                    )
                     .map(|edit| {
                         let edit_start = edit.new.start.0;
                         let edit_end = edit_start + (edit.old.end.0 - edit.old.start.0);