Add Regexp-Regexp Alternative operator for Grammar DSL

Author: vkutuev

solver/src/main/kotlin/org/ucfs/grammar/combinator/extension/StringExtension.kt

@@ -19,11 +19,12 @@ object StringExtension {
     infix fun String.or(other: String): Regexp = Alternative.makeAlternative(left = Term(this), Term(other))
     infix fun String.or(other: Regexp): Regexp = Alternative.makeAlternative(left = Term(this), other)
     infix fun Regexp.or(other: String): Regexp = Alternative.makeAlternative(left = this, Term(other))
+    infix fun Regexp.or(other: Regexp): Regexp = Alternative.makeAlternative(left = this, other)
 
 
     fun many(some: String): Regexp {
         return many(Term(some))
     }
     fun Option(exp: String) = Alternative.makeAlternative(Epsilon, Term(exp))
 
-}
+}