Previously, the `URLS_TO_REDIRECT.txt` file was expected to separate
URLs by a `\t` character. This could easily been mistaken for a regular
space and would often result in test errors when updating the file.
This commit updates the `URLS_TO_REDIRECT.txt` file and the
corresponding test helpers to use `-->` (potentially surrounded by
whitespace) as a separator for the URLs. This also gives a hint about
the "from" --> "to" relationship of the redirect URL pair.
PR Close#41680
13913231f1