HPCC-19140 Test case for fileposition and PERSIST

Signed-off-by: Gavin Halliday <gavin.halliday@lexisnexis.com>

ecl/regress/issue19140.ecl

@@ -0,0 +1,15 @@
+r1 := { STRING10 x };
+
+r := RECORD(r1)
+   UNSIGNED filepos{virtual(fileposition)};
+END;
+
+dsin := dataset(['One','','Two','','Three','','Four','','Five','','Six','','Seven','','Eight','','Nine','','Ten',''], r1);
+ds := DATASET('~regress::one_to_ten', r, thor);
+p := ds(x != '') : PERSIST('noblanks');
+filtered := p(filepos < 100);
+
+sequential(
+    output(dsin,,'~regress::one_to_ten',overwrite);
+    output(filtered);
+);