[#139] Ensure all emails send same message

[matthewhilton]

Closes #139

Changes:

• Ensures that regardless if you send ical, text, or both the contents of the email received is the same. Previously, the ical email would send the plaintext as html leading to clients showing everything on a single line.
• This is done by only passing in text to the email_to_user function, and allowing it to convert it to the appropriate html. This fixes a lot of the missing newline issues.

Note: This PR does not attempt to cleanup / fix formatting issues in email. It purely attempts to ensure that the emails sent (ical or not) are the same and fix the newline issue. Fixing email formatting is covered by #176

Testing

• Covered by new unit tests (previously were no email related unit tests)

Manual testing:

Email	Before	After
Confirmation iCal
Cancellation

To Do:

• Ci upstream fix - waiting for upstream nvm issue to be resolved
• Cherry pick to latest branch [#139] Ensure all emails send same message #178
• Test manually that emails are formatted decently

[keevan]

The function str_contains() is not present in PHP version 7.4 or earlier
(PHPCompatibility.FunctionUse.NewFunctions.str_containsFound)

I checked and 4.1 has a min version of php 7.4, whereas Moodle 4.0 has a min version of php 7.3, so str_contains might not be a compatible function for this branch.

Similarly for ??=

The null coalesce equal operator (??=) is not present in PHP version 7.3 or earlier
(PHPCompatibility.Operators.NewOperators.t_coalesce_equalFound)

and the fn keyword

The "fn" keyword for arrow functions is not present in PHP version 7.3 or earlier
(PHPCompatibility.Keywords.NewKeywords.t_fnFound)

Kind of annoying, and this wouldn't have been an issue for a MOODLE_401_STABLE branch.

Otherwise, tests look good, changes look good.

[danmarsden]

Just create a 4.1 branch, we don't officially support 4.0 now anyway.

[matthewhilton]

Thanks @keevan good pickups, i've added the php version compatibility checker to my tooling now as well.

Deciding between forking a new branch and fixing up the issues, I decided to just fix up the issues manually since they were tiny and easy to tweak. Making a whole new branch seems unnecessary to me in this case.