Compare forbidCustomFunctions with spaze/phpstan-disallowed-calls

[janedbal]

This MR uses tests of our forbidCustomFunctions against logic in spaze/phpstan-disallowed-calls and changes the test files to display the diff of the behaviour.

Assuming our tests are correct then disallowed-calls reports:

• false negative for any red diff (error removed)
• false positive for any green diff (error added)