Site Health: Display the original PHP memory limit on Site Health Info screen.

This ensures that if the limit has been modified for admin screens by `wp_raise_memory_limit()`, the original value is displayed along with the current value.

Props Clorith, espiat, zodiac1978, SergeyBiryukov.
Fixes #49329.
Built from https://develop.svn.wordpress.org/trunk@47762


git-svn-id: https://core.svn.wordpress.org/trunk@47538 1a063a9b-81f0-0310-95a4-ce76da25c4cd