[REF] Convert _checkAccess to event listener

[colemanw]

Overview

Fixes a FIXME that @totten left for me to fix in #20533

Also see https://lab.civicrm.org/dev/core/-/issues/4887

Before

// Note: $bao::_checkAccess() is a quasi-listener. TODO: Convert to straight-up listener.

After

Straight-up listener

[civibot]

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[artfulrobot]

@colemanw I've read it through but not r-run it. I can see the tests pass, so insofar as we had test coverage for this then things look good. I'm not entirely sold on the event listener model for this: it seems to be a bit less clear (order of execution, reading the code is now a case of hunting for listeners) and it introduces a longer codepath to achieve the same thing, though I'm sure it's not enough to make a huge/noticeable difference, it's still more.

[colemanw]

@artfulrobot I'm not entirely sold on the event listener model for this

I think the argument is that event listeners are standard across symfony-compatible php apps, whereas random-function-with-magic-name-that-starts-with-an-underscore-for-some-reason is just a weird little thing I made-up. So this takes us more in the standards-direction and also gets rid of the "two different ways of doing the same thing" motif which can be confusing to devs. And I'm not too attached to my weird little underscore-function to kill it off if it makes things more sane.

[colemanw]

@artfulrobot I wasn't sure about test coverage either so I did a couple test runs locally and a draft commit while writing this pr just to make sure that if any of these conversions wasn't working properly at least one test would fail somewhere... and one did.
I would feel better if it was more than one! But it's something.

[artfulrobot]

ok, over to you to merge then 👍