`std::borrow::Cow<'_, str>` now implements `TextBuffer` (#3164)

* `std::borrow::Cow<'_, str>` now implements `TextBuffer`

* Add pr number

* Remove line from CHANGELOG.md

* Add missing semicolons

* remove extra semicolon

---------

Co-authored-by: Emil Ernerfeldt <emil.ernerfeldt@gmail.com>

crates/egui/src/widgets/text_edit/text_buffer.rs

@@ -1,4 +1,4 @@
-use std::ops::Range;
+use std::{borrow::Cow, ops::Range};
 
 /// Trait constraining what types [`crate::TextEdit`] may use as
 /// an underlying buffer.
@@ -100,6 +100,36 @@ impl TextBuffer for String {
     }
 }
 
+impl<'a> TextBuffer for Cow<'a, str> {
+    fn is_mutable(&self) -> bool {
+        true
+    }
+
+    fn as_str(&self) -> &str {
+        self.as_ref()
+    }
+
+    fn insert_text(&mut self, text: &str, char_index: usize) -> usize {
+        <String as TextBuffer>::insert_text(self.to_mut(), text, char_index)
+    }
+
+    fn delete_char_range(&mut self, char_range: Range<usize>) {
+        <String as TextBuffer>::delete_char_range(self.to_mut(), char_range);
+    }
+
+    fn clear(&mut self) {
+        <String as TextBuffer>::clear(self.to_mut());
+    }
+
+    fn replace(&mut self, text: &str) {
+        *self = Cow::Owned(text.to_owned());
+    }
+
+    fn take(&mut self) -> String {
+        std::mem::take(self).into_owned()
+    }
+}
+
 /// Immutable view of a `&str`!
 impl<'a> TextBuffer for &'a str {
     fn is_mutable(&self) -> bool {