[5.1] webservices plugins use concrete event classes

[heelc29]

Summary of Changes

use concrete event classes for webservices plugins introduced with #40522

Testing Instructions

test API endpoints
(many plugins/endpoints are also tested by system tests)

Actual result BEFORE applying this Pull Request

webservices plugins use legacy listeners

Expected result AFTER applying this Pull Request

webservices plugins use SubscriberInterface and concrete events (actual coding standard)

Link to documentations

Please select:

• No documentation changes for docs.joomla.org needed
• No documentation changes for manual.joomla.org needed

[bembelimen]

I have tested this item ✅ successfully on 96c46e4

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[LadySolveig]

Thank you @heelc29