[Attributor] Unify testing (=updates,prefixes,run configurations,...)

When the Attributor was created the test update scripts were not well
suited to deal with the challenges of IR attribute checking. This
partially improved.

Since then we also added three additional configurations that need
testing; in total we now have the following four:
{ TUNIT, CGSCC } x { old pass manager (OPM), new pass manager (NPM) }

Finally, the number of developers and tests grew rapidly (partially due
to the addition of ArgumentPromotion and IPConstantProp tests), which
resulted in tests only being run in some configurations, different
prefixes being used, and different "styles" of checks being used.

Due to the above reasons I believed we needed to take another look at
the test update scripts. While we started to use them, via UTC_ARGS:
--enable/disable, the other problems remained. To improve the testing
situation for *all* configurations, to simplify future updates to the
test, and to help identify subtle effects of future changes, we now use
the test update scripts for (almost) all Attributor tests.

An exhaustive prefix list minimizes the number of check lines and makes
it easy to identify and compare configurations.

Tests have been adjusted in the process but we tried to keep their
intend unchanged.

Reviewed By: sstefan1

Differential Revision: https://reviews.llvm.org/D76588

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