[test] Add a fixed stress tester issue

This is no longer too complex.

Author: hamishknight

validation-test/IDE/stress_tester_issues_fixed/issue-66785.swift

@@ -0,0 +1,5 @@
+// RUN: %batch-code-completion
+// https://github.com/swiftlang/swift/issues/66785
+
+0...31127...159768...8791155...11591160...11611425...14691471...14711473...14741476...14771479...#^COMPLETE^#
+// COMPLETE: Literal[Integer]/None: 0[#Int#]; name=0