[libc] Add index operator[] to StringView

GitOrigin-RevId: 03375089f5a66a5fa4dc7b30e6b62e7e69086226
diff --git a/utils/CPP/StringView.h b/utils/CPP/StringView.h
index 2e7b3a0..52f61a0 100644
--- a/utils/CPP/StringView.h
+++ b/utils/CPP/StringView.h
@@ -45,6 +45,8 @@
 
   size_t size() { return Len; }
 
+  const char &operator[](size_t Index) const { return Data[Index]; }
+
   StringView remove_prefix(size_t N) const {
     if (N >= Len)
       return StringView();