[5.4] Convert mod_whosonline to service provider

[joomlaweby]

Summary of Changes

Converts the who is online site module to service provider.

Testing Instructions

1. Make sure you have site module mod_whosonline published
2. You should see module output

Actual result BEFORE applying this Pull Request

Module works as expected

Expected result AFTER applying this Pull Request

Module works same way as before applying pull request

Link to documentations

Please select:

• Documentation link for docs.joomla.org:

• No documentation changes for docs.joomla.org needed

• Pull Request link for manual.joomla.org:

• No documentation changes for manual.joomla.org needed

[ghazal]

I have tested this item ✅ successfully on 886678d

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[hans2103]

I have tested this item ✅ successfully on 886678d

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_{This comment was created with the J!Tracker Application at issues.joomla.org/tracker/joomla-cms/45775.}

[exlemor]

I have tested this item ✅ successfully on 886678d

I have successfully tested this on Chrome, Firefox, Safari.

(Unrelated to this PR but Heiko and I discovered a potential bug or at least odd behavior in Safari 18.x+ with the Who's Online module (with or without the PR applied) where if you reload the front-end page it increments by 1 the number of Who's Online guests even though there is still just you browsing the site - it may be because of a protective feature of Safari..)

Interestingly, (I checked the database) while the session_id is different each time the 820 byte data that is in the data field is IDENTICAL.

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[richard67]

RTC

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[muhme]

Final test before merge, before applying this PR, with JBT graft Joomla_5.4.0-alpha4-dev-Development-Full_Package.zip:

• Tested to display '# of Guests / Users', 'Usernames' and 'Both'

Tested with this PR by graft Joomla_5.4.0-alpha4-dev+pr.45775-Development-Full_Package.zip:

• ✅ Tested to display '# of Guests / Users', 'Usernames' (with no one logged in -> empty and one login) and 'Both'
• Installed German language paket as extension and switched to default German
• ✅ Tested to display Who's Online with German translations

[muhme]

Thank you @joomlaweby for your contribution. Thank you @ghazal, @hans2103 and @exlemor for testing.