Loss of robustness on block comments since update 4.2

Update 4.2 brought some improvements in parsing execution results into comments.
However, it also came with a minor drawback: block comments are less robust to whitespaces.

Now, block comments must start and end with lines containing exactly <|-- and --|> with no whitespaces around whatsoever.
If these lines contain whitespaces, the whole block will not be shown to students.

I'm logging this as an issue because it breaks activities that were working fine before.

jcrodriguez-dis / moodle-mod_vpl

Loss of robustness on block comments since update 4.2 #168