PR #66461 introduced a regression that resulted in an in correct block in the file
if the block to be inserted did not end with a line separator. Fix this bug and add
tests to cover this scenario.
Fixes#64966
* Fix "TypeError: splitlines() takes no keyword arguments" on Python2.7
* Add changelog fragment
* Don't use `grep -P` for BSD/macOS compatibility
* Fix sanity checks complaining about test fixtures with mixed line endings
* Update changelogs/fragments/66461-blockinfile_preserve_line_endings.yaml
This prevents a stack trace in Python 3 when the result is an empty file since
the file is open in binary mode and a native string in Python 3 is str,
not bytes.
A preliminary set of test targets for "core" supported module that had no independent tests. These will also help us ensure python3 compatibility for those modules and prevent future regressions.
