[BUGFIX] Prevent exclude field mixup in FromEngine

Use a local variable for storing the excluded fields in the
FormEngine to prevent the configuration from being overwritten
by the inline form element renderer.

Fixes: #47359
Releases: 6.1, 6.0, 4.7, 4.5
Change-Id: I5a7a2de16d767f854b4d3f89d599deec28266092

Conflicts:
	typo3/sysext/backend/Classes/Form/FormEngine.php