Docs: Fix the syntax for a parameter notation and separately add a missing...

Docs: Fix the syntax for a parameter notation and separately add a missing return notation for two `POMO_Reader` methods.

Props subrataemfluence.
Fixes #44422.

Built from https://develop.svn.wordpress.org/trunk@44326


git-svn-id: https://core.svn.wordpress.org/trunk@44156 1a063a9b-81f0-0310-95a4-ce76da25c4cd