Provide a mechanic for popping off items from a list

Think I can just try realizing the suggested action.

Added two new actions for list operations, and a new condition plugin "Token: exists". Using these components, I'm able to iterate over a list without using custom events.

Had to refator the DataTransferObject a bit and also fixed a possible infinite loop for dependency calculation when creating a cyclic graph representing a loop in BPMN.

I've found another possible action plugin that may be useful regarding list operations: Putting an entity onto a list. Will add that into this MR.

The only thing that could be cherry-picked for 1.0.x from this MR is the following commit:
https://git.drupalcode.org/project/eca/-/merge_requests/209/diffs?commit...
That includes the prevention of an infinite loop during dependency calculation.

All others are feature additions and therefore belong into 1.1.x.

Will have a look

Setting to review for continuation discussing the last note.

That's great, thanks for that. Tests are green on my system, which looks like both your and my expectations are met by the current implementation - unless the test coverage is not complete yet (?)

I think you need to enable test runs for the 1.1.x branch.

Setting to needs work, now that a test is failing.

Let's look at the test that is currently failing:

<?php
$condition = $this->conditionManager->createInstance('eca_token_exists', [
      'token_name' => '[placeholder]',
    ]);
    $this->assertFalse($condition->evaluate(), "Placeholder should not exist");
    $this->tokenServices->addTokenData('placeholder', 'mytoken1');
    $this->assertTrue($condition->evaluate(), "Placeholder now should exist");
    $this->tokenServices->addTokenData('placeholder', 'mytoken3');
    $this->assertFalse($condition->evaluate(), "Placeholder should not exist"); // <- This one is failing
?>

The reason why this is failing, is because

<?php
$this->tokenServices->addTokenData('placeholder', 'mytoken3');
?>

is adding the string "mytoken3" as token data for token name "placeholder". The condition then says "Yes, it exists" because there is token data, in this case a DTO holding "mytoken3" as string representation value, and token replacement would replace "Thevalue: [placeholder]" to "Thevalue: mytoken3".

Would changing the above mentioned line to

$this->tokenServices->addTokenData('placeholder', $this->tokenServices->getTokenData('mytoken3'));

do what you want to reflect here as a use case? As an alternative, you could also make use of an action that represents your case, like "Token: set value". But I currently doubt that the current test case is properly reflecting your targeted use case, as it's adding a string to the Token stack as described above, instead of representing another token name.

Reading #21, this looks like you expect the "token_name" input to support tokens. Currently, none of our plugins supports token replacement in that input, and the new condition in this MR would be the very first one supporting it.

I'd recommend to see this as a separate feature request, because for that we'd have to look at all other plugins making use of "token_name" and change the overall behavior to keep consistency accross all plugins. Cleary an issue on its own.