feat(parser): expand Parser

src/main/kotlin/kestrel/sql/parser/Parser.kt

@@ -1805,4 +1805,20 @@ class Parser(private val tokens: List<Token>) {
 
     private fun describe(token: Token): String =
         if (token.type == TokenType.EndOfInput) "end of input" else token.lexeme
+
+    private companion object {
+        val AGGREGATE_FUNCTIONS = setOf("COUNT", "SUM", "AVG", "MIN", "MAX")
+        val WINDOW_RANKING_FUNCTIONS = mapOf(
+            "ROW_NUMBER" to WindowFunctionKind.RowNumber,
+            "RANK" to WindowFunctionKind.Rank,
+            "DENSE_RANK" to WindowFunctionKind.DenseRank
+        )
+        val WINDOW_OTHER_FUNCTIONS = mapOf(
+            "LAG" to WindowFunctionKind.Lag,
+            "LEAD" to WindowFunctionKind.Lead,
+            "FIRST_VALUE" to WindowFunctionKind.FirstValue,
+            "LAST_VALUE" to WindowFunctionKind.LastValue,
+            "NTILE" to WindowFunctionKind.Ntile
+        )
+    }
 }