[PlSql] Break out unary_logical_operation rule and allow not more than one unary_logical_operation per unary_logical_expression (#3811)

To simplify processing of multiple unary logical operations
within a `unary_logical_expression`, as well as to avoid ambiguity
of NOT tokens `within unary_logical_expression`.

Previously "foo IS NULL IS NOT NAN" would be allowed.

Author: marty-se

sql/plsql/PlSqlParser.g4

@@ -6083,7 +6083,11 @@ logical_expression
     ;
 
 unary_logical_expression
-    : NOT? multiset_expression (IS NOT? logical_operation)*
+    : NOT? multiset_expression unary_logical_operation?
+    ;
+
+unary_logical_operation
+    : IS NOT? logical_operation
     ;
 
 logical_operation:

sql/plsql/examples-sql-script/logical_expressions.sql

@@ -0,0 +1,17 @@
+DECLARE
+    FOO NUMBER := 1;
+    BAR NUMBER := 2;
+BEGIN
+    IF FOO = 1 AND BAR IS NOT NULL THEN
+        RAISE_APPLICATION_ERROR(-20001, 'FOO is 1 and BAR is not null');
+    END IF;
+
+    IF FOO = 1 OR NOT BAR IS NULL THEN
+        RAISE_APPLICATION_ERROR(-20002, 'FOO is 1 or BAR is not null');
+    END IF;
+
+    IF FOO = 1 AND BAR IS NOT NULL AND BAR IS NOT NAN THEN
+        RAISE_APPLICATION_ERROR(-20003, 'FOO is 1 and BAR is not null and BAR is not nan');
+    END IF;
+END;
+/