Change default of FlattenerConfiguration.allowSpecializationAfterExclusion

[J3173]

In Release v3.2.0 is stated:

v3.2.0 reverts this correct behaviour to the pre-v3.1.0 behaviour. It introduces a config variable for this: FlattenerConfiguration.allowSpecializationAfterExclusion. WIthin this major version of Archie, the default will be set to true as setting this to false is in theory backwards incompatible.

We should check if this is still needed and do this.

[J3173]

It turns out this is more complicated than I thought. The Flattener is used by the ArchetypeValidator and the ADL14Converter, and there is currently now way to set the allowSpecializationAfterExclusion setting for those use cases.

We decided to leave this issue out of the Archie 4 release, as it is not essential for that release.