Support rich text convert from cow-string. (#1774)

egui/src/widget_text.rs

@@ -1,3 +1,4 @@
+use std::borrow::Cow;
 use std::sync::Arc;
 
 use crate::{
@@ -65,6 +66,13 @@ impl From<String> for RichText {
     }
 }
 
+impl From<Cow<'_, str>> for RichText {
+    #[inline]
+    fn from(text: Cow<'_, str>) -> Self {
+        Self::new(text)
+    }
+}
+
 impl RichText {
     #[inline]
     pub fn new(text: impl Into<String>) -> Self {
@@ -605,6 +613,13 @@ impl From<String> for WidgetText {
     }
 }
 
+impl From<Cow<'_, str>> for WidgetText {
+    #[inline]
+    fn from(text: Cow<'_, str>) -> Self {
+        Self::RichText(RichText::new(text))
+    }
+}
+
 impl From<RichText> for WidgetText {
     #[inline]
     fn from(rich_text: RichText) -> Self {