[PHPUnit 10] Provide a static alternative to @dataproviders using PHPUnit mocks in CommentLinkBuilderTest and MailHandlerTest

Problem/Motivation

PHPUnit 10 deprecates use of non-static @dataProvider methods. This means that @dataProvider methods can no longer make calls to non-static methods. Any non-static call ($this->someMethod()) needs to be replaced by a call to a static alternative (static::someOtherMethod()), that would have to be implemented if not available.

In this issue, focus on replacing usage of PHPUnit mocks in CommentLinkBuilderTest and MailHandlerTest

Proposed resolution

Following up on #3365331: [PHPUnit 10] Provide a static alternative to ConfigMapperManagerTest::providerTestHasTranslatable, replace usage of PHPUnit mocks with PHPSpec prophecies instead, wherever possible.

Remaining tasks

User interface changes

API changes

Data model changes

Release notes snippet