Heartbeat: Do not disable the login prompts when the user needs to log in...

Heartbeat: Do not disable the login prompts when the user needs to log in again but has closed the log in modal. Add a 5 minutes timeout before asking them to log in again.

Props dsixinetu, adamsilverstein, azaozz.
Fixes #49573.
Built from https://develop.svn.wordpress.org/trunk@48337


git-svn-id: https://core.svn.wordpress.org/trunk@48106 1a063a9b-81f0-0310-95a4-ce76da25c4cd