Fix expansion filter for content added in later patches

[DWalland]

Summary

Update the Retail expansion filter to prefer an object's
expansionID before falling back to awp value.

Problem

Some content belongs to an older expansion but was added or reworked in a
later expansion's patch.

For example, for Siege of Orgrimmar loot to show up you need to have both the MoP and WoD filter on.
some of its difficulty data has awp=60002 because it was added with the Warlords of
Draenor pre-patch. The expansion filter interpreted that value as WoD content.

As a result, Siege of Orgrimmar was hidden when:

• Mists of Pandaria was enabled
• Warlords of Draenor was disabled

This also fixes #2344 where Legion content shows up if all filters are disabled.

Fix

When an object is nested under an expansion wrapper, the filter now uses the
inherited expansionID to determine visibility. For objects without an
expansion wrapper, it retains the existing awp-based fallback.

This means Siege of Orgrimmar correctly follows the MoP filter without
changing the behavior of unscoped content.

Verification

• Verified in-game with MoP enabled and WoD disabled

Scope

This applies to nested content generally, not only Siege of
Orgrimmar. The containing expansion identifies the content's expansion
ownership, while awp identifies when a particular object was added or
reworked.

[DWalland]

After some testing i still found some items where you needed to have two expansion filters enabled for them to show up. (Like guild mount/tabards from MoP was under the Cata 'Guild Vendor' category. Or 'Chamber of Heart from BfA which was under 'Silithus: The Wound' from Legion.) Now it filters based on the leaf/end items expansion.
Every item from a expansion should be viewable with only the single correct expansion filter enabled.