Add a RuneLit alias for CharLit

Also change the doc comment on CharLit to RuneLit

ql/src/semmle/go/Expr.qll

@@ -218,10 +218,12 @@ class FloatLit extends @floatlit, BasicLit { }
 class ImagLit extends @imaglit, BasicLit { }
 
 /**
- * A character literal.
+ * A rune literal.
  */
 class CharLit extends @charlit, BasicLit { }
 
+class RuneLit = CharLit;
+
 /**
  * A string literal.
  */