Swift: Add demonstrative test case.

Author: geoffw0

swift/ql/test/query-tests/Security/CWE-1333/ReDoS.expected

@@ -2,6 +2,7 @@
 | ReDoS.swift:65:22:65:22 | a* | This part of the regular expression may cause exponential backtracking on strings containing many repetitions of 'a'. |
 | ReDoS.swift:66:22:66:22 | a* | This part of the regular expression may cause exponential backtracking on strings containing many repetitions of 'a'. |
 | ReDoS.swift:69:18:69:18 | a* | This part of the regular expression may cause exponential backtracking on strings containing many repetitions of 'a'. |
-| ReDoS.swift:75:46:75:46 | a* | This part of the regular expression may cause exponential backtracking on strings containing many repetitions of 'a'. |
-| ReDoS.swift:77:57:77:57 | a* | This part of the regular expression may cause exponential backtracking on strings containing many repetitions of 'a'. |
-| ReDoS.swift:80:57:80:57 | a* | This part of the regular expression may cause exponential backtracking on strings containing many repetitions of 'a'. |
+| ReDoS.swift:73:26:73:33 | (?:.\|\\n)* | This part of the regular expression may cause exponential backtracking on strings starting with 'isx' and containing many repetitions of '\\n'. |
+| ReDoS.swift:77:46:77:46 | a* | This part of the regular expression may cause exponential backtracking on strings containing many repetitions of 'a'. |
+| ReDoS.swift:79:57:79:57 | a* | This part of the regular expression may cause exponential backtracking on strings containing many repetitions of 'a'. |
+| ReDoS.swift:82:57:82:57 | a* | This part of the regular expression may cause exponential backtracking on strings containing many repetitions of 'a'. |

swift/ql/test/query-tests/Security/CWE-1333/ReDoS.swift

@@ -70,6 +70,8 @@ func myRegexpTests(myUrl: URL) throws {
     let regex = try Regex(str)
     _ = try regex.firstMatch(in: tainted)
 
+    _ = try Regex(#"(?is)X(?:.|\n)*Y"#) // BAD - suggested attack should begin with 'x' or 'X', *not* 'isx' or 'isX' [WRONG]
+
     // NSRegularExpression
 
     _ = try? NSRegularExpression(pattern: "((a*)*b)") // DUBIOUS (never used) [FLAGGED]