[PHPDoc] Improved ContentService doc for API reference

[adriendupuis]

🎫 Issue	N/A

Description:

Enhance ContentService doc:

• Rewording (e.g. ContentService::loadContent)
• Format PHPDoc (capitalize description except @thows, trailing period, etc.)
• Enhance a bit (add few @see, etc.)

PHP API Reference output:

• Preview rendering of those changes in PHP API Reference: https://ez-systems-developer-documentation--2413.com.readthedocs.build/en/2413/api/php_api/php_api_reference/classes/Ibexa-Contracts-Core-Repository-ContentService.html
• Compare with current 4.6.7: https://doc.ibexa.co/en/latest/api/php_api/php_api_reference/classes/Ibexa-Contracts-Core-Repository-ContentService.html

Notice that by inheritance, it also changes the doc for ContentServiceDecorator:

• https://ez-systems-developer-documentation--2413.com.readthedocs.build/en/2413/api/php_api/php_api_reference/classes/Ibexa-Contracts-Core-Repository-Decorator-ContentServiceDecorator.html
• https://doc.ibexa.co/en/latest/api/php_api/php_api_reference/classes/Ibexa-Contracts-Core-Repository-Decorator-ContentServiceDecorator.html

For QA:

Documentation:

[adamwojs]

@adriendupuis Could you please address issues reported by phpstan?

[alongosz]

@adriendupuis this one needs rebase. Are all prior review remarks resolved and is it ready for another round of review?

[sonarqubecloud]

Quality Gate passed

Issues
0 New issues
0 Accepted issues

Measures
0 Security Hotspots
0.0% Coverage on New Code
0.0% Duplication on New Code

See analysis details on SonarCloud

[konradoboza]

As long as https://github.com/ibexa/core/pull/379/files#r1828007119 and similar are applied.

[sonarqubecloud]

Quality Gate passed

Issues
0 New issues
0 Accepted issues

Measures
0 Security Hotspots
0.0% Coverage on New Code
0.0% Duplication on New Code

See analysis details on SonarCloud