Generalize pasting when number of selections doesn't match clipboard's

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

zed/src/editor/buffer/anchor.rs

@@ -69,6 +69,28 @@ impl Anchor {
                 .then_with(|| self_bias.cmp(other_bias)),
         })
     }
+
+    pub fn bias_left(&self, buffer: &Buffer) -> Result<Anchor> {
+        match self {
+            Anchor::Start
+            | Anchor::Middle {
+                bias: AnchorBias::Left,
+                ..
+            } => Ok(self.clone()),
+            _ => buffer.anchor_before(self),
+        }
+    }
+
+    pub fn bias_right(&self, buffer: &Buffer) -> Result<Anchor> {
+        match self {
+            Anchor::End
+            | Anchor::Middle {
+                bias: AnchorBias::Right,
+                ..
+            } => Ok(self.clone()),
+            _ => buffer.anchor_after(self),
+        }
+    }
 }
 
 pub trait AnchorRangeExt {

zed/src/editor/buffer/mod.rs

@@ -2264,6 +2264,12 @@ impl ToOffset for Anchor {
     }
 }
 
+impl<'a> ToOffset for &'a Anchor {
+    fn to_offset(&self, buffer: &Buffer) -> Result<usize> {
+        Ok(buffer.summary_for_anchor(self)?.chars)
+    }
+}
+
 pub trait ToPoint {
     fn to_point(&self, buffer: &Buffer) -> Result<Point>;
 }