ObjectDeclarations::getDeclaredProperties(): improve documentation #1863

Job	Run time
Basic CS and QA checks	33s
Lint Markdown / Lint Markdown	7s
PHPStan / PHPStan	3m 8s
QA Markdown / QA Markdown	1m 39s
Lint Yaml / Lint Yaml	4s
Lint Yaml / Check GHA workflows	5s
	5m 36s

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