[FEA] Re-instate "transpile complex regex 2" test in some form

[andygrove]

Is your feature request related to a problem? Please describe.
In PR #5610 the following test was ignored. This is a follow on issue to decide what to do with this test. Maybe it needs modifying and kept as a general test for the transpiler.

  // this was a test for transpiling but we did not ever try to run the
  // resulting regex to see if it produced valid results
  ignore("transpile complex regex 2") {
    val TIMESTAMP_TRUNCATE_REGEX = "^([0-9]{4}-[0-9]{2}-[0-9]{2} " +
      "[0-9]{2}:[0-9]{2}:[0-9]{2})" +
      "(.[1-9]*(?:0)?[1-9]+)?(.0*[1-9]+)?(?:.0*)?\\z"

    // input and output should be identical except for `.` being replaced 
    // with `[^\n\r\u0085\u2028\u2029]` and `\z` being replaced with `$`
    doTranspileTest(TIMESTAMP_TRUNCATE_REGEX,
      TIMESTAMP_TRUNCATE_REGEX
        .replaceAll("\\.", "[^\n\r\u0085\u2028\u2029]")
        .replaceAll("\\\\z", "\\$"))
  }

Describe the solution you'd like
TBD

Describe alternatives you've considered
None

Additional context
None