[!!!][FEATURE] Allow reloading of backend topbar

A new API is introduced that allows to reload the backend’s topbar.
The reload may be triggered via JavaScript and PHP.

As the registered events of the toolbar items within the topbar get lost
after reloading, the event registration for these toolbar items needs
some adoption.

The topbar is now reloaded in case of:
- updating the user's avatar
- after configuring an extension
- opening the EXT:belog module from the System Information menu

Resolves: #79196
Releases: master
Change-Id: Ib6b65d7327c9db2b818ad9ad549cb2f2f00d1595
Reviewed-on: https://review.typo3.org/51183


Tested-by: TYPO3com <no-reply@typo3.com>
Reviewed-by: Benni Mack <benni@typo3.org>
Reviewed-by: Georg Ringer <georg.ringer@gmail.com>
Tested-by: Georg Ringer <georg.ringer@gmail.com>