regex: add as_match method to Captures trait

Ref rust-lang/regex#1146

PR #2898

crates/matcher/src/lib.rs

@@ -389,6 +389,15 @@ pub trait Captures {
     /// for the overall match.
     fn get(&self, i: usize) -> Option<Match>;
 
+    /// Return the overall match for the capture.
+    ///
+    /// This returns the match for index `0`. That is it is equivalent to
+    /// `get(0).unwrap()`
+    #[inline]
+    fn as_match(&self) -> Match {
+        self.get(0).unwrap()
+    }
+
     /// Returns true if and only if these captures are empty. This occurs
     /// when `len` is `0`.
     ///