[TASK] Priority is not execution order in for Extractors

When the meta-data extraction services have been introduced it
silently has been assumed that the defined priority can be
used as execution order. In fact the priority just defines which
data takes precedence of another. In fact you might have an
extraction service which has highest priority for the fields it
serves but on the opposite should run as first, so other
extraction services already can use the data.

This change adds a second "priority" for that purpose and adapts
the indexing process accordingly.

Resolves: #54228
Releases: 6.2
Change-Id: I649fc8b91103ab518e5a692bf73c54851e8b70b1
Reviewed-on: https://review.typo3.org/26696
Reviewed-by: Frans Saris
Reviewed-by: Wouter Wolters
Reviewed-by: Stefan Neufeind
Reviewed-by: Ingo Schmitt
Reviewed-by: Steffen Ritter
Tested-by: Steffen Ritter