[TASK] Further clean ups in extension manager code

Extension Manager Utility classes are optimized for further
clean ups:
- "ext_icon" in package array is renamed to "icon" with an absolute path
- unneeded icon information is removed
- EmConfUtility has optimized signature for handing in the extension key
- Minor optimizations in naming of arguments in FileHandlingUtility
- Dumping an extension.zip to the browser is now within the ActionController
- Various public properties are now protected

As this is just another incremental way to streamline Extension Manager
code, please note that e.g. strict types will follow in follow up patches.

Resolves: #90033
Releases: master
Change-Id: I6d53d850f4307581a82d6d7ec3933c9592573f23
Reviewed-on: https://review.typo3.org/c/Packages/TYPO3.CMS/+/62783


Tested-by: TYPO3com <noreply@typo3.com>
Tested-by: Daniel Goerz <daniel.goerz@posteo.de>
Tested-by: Susanne Moog <look@susi.dev>
Reviewed-by: Jörg Bösche <typo3@joergboesche.de>
Reviewed-by: Steffen Frese <steffenf14@...>