Parameter description in update_post_meta()

[stevenlinx]

Parameter descriptions should be updated/migrated from Codex.

Codex:
​https://codex.wordpress.org/Function_Reference/update_post_meta

DevHub:
​https://developer.wordpress.org/reference/functions/update_post_meta/

[SergeyBiryukov]

In 48214:

Docs: Improve documentation for the $prev_value parameter and return result of various metadata update functions.

Props stevenlinx.
Fixes #50502. See #49572.

[SergeyBiryukov]

Thanks for the patch! The $prev_value and @return improvements are now in.

I'm less inclined to add that the meta key and value should be raw and not sanitized, as it's not mentioned in other similar functions and doesn't seem to come up often. If someone feels strongly about that, feel free to reopen.