[TASK] EM: Reduce dependencies when writing t3x files

The method unpackExtensionFromExtensionDataArray()
is only used once, but with the second argument
set to "null", so all complexity down to EmConfUtility
is reduced.

Same goes for `isValidExtensionPath` in FileHandlingUtility
which is not related to FileHandlingUtility and does not
need to be exposed.

Resolves: #93059
Releases: master
Change-Id: I035e2faa81d6312c09ae5d040335784ec389f7c5
Reviewed-on: https://review.typo3.org/c/Packages/TYPO3.CMS/+/67093


Tested-by: TYPO3com <noreply@typo3.com>
Tested-by: Oliver Bartsch <bo@cedev.de>
Tested-by: Georg Ringer <georg.ringer@gmail.com>
Reviewed-by: Oliver Bartsch <bo@cedev.de>
Reviewed-by: Georg Ringer <georg.ringer@gmail.com>