Implement Anchor, AnchorRangeMap, SelectionSet in multi_buffer

Co-Authored-By: Nathan Sobo <nathan@zed.dev>

crates/text/src/anchor.rs

@@ -1,6 +1,5 @@
+use super::{FromAnchor, FullOffset, Point, ToOffset};
 use crate::{rope::TextDimension, BufferSnapshot};
-
-use super::{Buffer, FromAnchor, FullOffset, Point, ToOffset};
 use anyhow::Result;
 use std::{
     cmp::Ordering,
@@ -99,7 +98,7 @@ impl Anchor {
         Ok(offset_comparison.then_with(|| self.bias.cmp(&other.bias)))
     }
 
-    pub fn bias_left(&self, buffer: &Buffer) -> Anchor {
+    pub fn bias_left(&self, buffer: &BufferSnapshot) -> Anchor {
         if self.bias == Bias::Left {
             self.clone()
         } else {
@@ -107,7 +106,7 @@ impl Anchor {
         }
     }
 
-    pub fn bias_right(&self, buffer: &Buffer) -> Anchor {
+    pub fn bias_right(&self, buffer: &BufferSnapshot) -> Anchor {
         if self.bias == Bias::Right {
             self.clone()
         } else {

crates/text/src/rope.rs

@@ -685,6 +685,15 @@ impl sum_tree::Summary for TextSummary {
     }
 }
 
+impl<'a> std::ops::Add<Self> for TextSummary {
+    type Output = Self;
+
+    fn add(mut self, rhs: Self) -> Self::Output {
+        self.add_assign(&rhs);
+        self
+    }
+}
+
 impl<'a> std::ops::AddAssign<&'a Self> for TextSummary {
     fn add_assign(&mut self, other: &'a Self) {
         let joined_chars = self.last_line_chars + other.first_line_chars;