Rollup merge of #58005 - vitiral:docs_trim_start_matches, r=Manishearth

update docs for fix_start/end_matches

fixes #57686:

src/libcore/str/mod.rs

@@ -3786,10 +3786,10 @@ impl str {
     ///
     /// # Text directionality
     ///
-    /// A string is a sequence of bytes. 'Left' in this context means the first
-    /// position of that byte string; for a language like Arabic or Hebrew
-    /// which are 'right to left' rather than 'left to right', this will be
-    /// the _right_ side, not the left.
+    /// A string is a sequence of bytes. `start` in this context means the first
+    /// position of that byte string; for a left-to-right language like English or
+    /// Russian, this will be left side; and for right-to-left languages like
+    /// like Arabic or Hebrew, this will be the right side.
     ///
     /// # Examples
     ///
@@ -3818,10 +3818,10 @@ impl str {
     ///
     /// # Text directionality
     ///
-    /// A string is a sequence of bytes. 'Right' in this context means the last
-    /// position of that byte string; for a language like Arabic or Hebrew
-    /// which are 'right to left' rather than 'left to right', this will be
-    /// the _left_ side, not the right.
+    /// A string is a sequence of bytes. `end` in this context means the last
+    /// position of that byte string; for a left-to-right language like English or
+    /// Russian, this will be right side; and for right-to-left languages like
+    /// like Arabic or Hebrew, this will be the left side.
     ///
     /// # Examples
     ///