Email body policy form should show available TWIG variables

Updated the title and description as it was misplaced with ✨ Email body policy form should show available TWIG variables Needs work .

@AdamPS, I added display of TWIG variables in the BodyEmailAdjuster.
But I would like to clarify, from which version it is better to note that getCommonAdjusters is deprecated, and in which version it should be removed?

Great thanks I'll take a look. It would be deprecated in 1.4.1 and removed in 2.0.0.

Yes it looks very good. I didn't have a chance to test it yet, however I reviewed the code in the MR and made a few simple comments.

@AdamPS, I made changes as per the comments in MR and added a deprecated message for MailerPolicyInterface::getCommonAdjusters.
If you have any other suggestions, I will be happy to add them.

Great thanks, it's better. I tested it now and I like it. I made some more comments in the MR - they should all be quick and easy.

Two bigger comments:

1) Variables can also be used in SubjectEmailAdjuster and we should do the same. Please put the code in a function (don't just copy it😃) e.g. MailerHelperInterface::showReplacementHelp()

2) It would be great to have a test. At the end of TestEmailTest::testTest(), add a call $this->submitForm([], 'Edit'); then can check that the page contains the replacement pattern for day.

Actually the are issues open to use tokens in other places too: e.g. plain text body or addresses. So perhaps we should have the variable/token helpers on the form just once - in PolicyEditForm, after all the adjusters. Then for each adjuster that accepts tokens/variables we can put a message to say that.

OK if you can do it for the email body then that's already good. We can raise a follow on issue for the other places.