Attribute.IsDefined is a perf hotsport during model building

[roji]

In #20135, building a user-submitted model shows a huge amount of time spent in Attribute.IsDefined, called from ForeignKeyAttributeConvention.FindForeignKeyAttributeOnProperty (and other conventions). I suspect that the inherit flag increases the perf cost, and the model in question seems to have quite a bit of hierarchy.

In addition, it seems like the same MemberInfo gets checked more than once; introducing a simple Dictionary<MemberInfo, bool> cache in ForeignKeyAttributeConvention for the results of Attribute.IsDefined reduced model building time from 79 to 45 seconds. After this I can still see other call-side for Attribute.IsDefined showing up (e.g. PropertyAttributeCOnventionBase) - we may want to investigate if it makes sense to be traversing the same members/entity types multiple times, and if so, consider adding caching.

[AndriySvyryd]

Duplicate of #13691

Also #214 will allow to remove the attribute conventions if attributes aren't used for model configuration.