Previously, LoggingApplicationListener its tests, and LogFile made some
assumptions that do not hold true on Windows. Specifically,
LoggingApplicationListenerTests used TestPropertySourceUtils to add
properties to the environment. This uses Java's standard Properties
parsing which does a poor job of handling Windows file paths (Strings
with backslashes in them). Secondly, LogFile made assumptions about
the use of forward clashes for the file separator.
This commit replaces the use of TestPropertySourceUtils and removes
the assumption about the OS's file separator.
Closes gh-15471
6adccbfd30