Portal: onRendered doesn't make sense if disablePortal is true

[Zaynex]

• This is not a v0.x issue.
• I have searched the issues of this repository and believe that this is not a duplicate.

Expected Behavior 🤔

I'm not sure if it's a design or a bug.
But I think this onRendered method should be allowed to be executed even if Portal is disablePortal. Otherwise, it can't be called a onRendered name(it's not inappropriate).

Current Behavior 😯

Portal: onRendered doesn't make sense if disablePortal is true.

Steps to Reproduce 🕹

Link:https://codesandbox.io/s/material-demo-q46iu

1. just click the MOUNT CHILDREN
2. see dev-tools console

The Reason

https://github.com/mui-org/material-ui/blob/783b6934632714a844b7d440e6d05729f9f2dc0c/packages/material-ui/src/Portal/Portal.js#L26

if disablePortal is true, it will not set mountNode.

https://github.com/mui-org/material-ui/blob/783b6934632714a844b7d440e6d05729f9f2dc0c/packages/material-ui/src/Portal/Portal.js#L34
and only if mountNode exist that onRendered function will call.

Your Environment 🌎

Tech	Version
Material-UI	latest
React	latest
Browser	chrome

[oliviertassinari]

@Zaynex We will deprecate onRendered in the future. Your problem should be handled in #16597.