Primal Clay (and the like) need a rework

[[Primal Clay]]

See discussion [here](https://github.com/magefree/mage/pull/9409#discussion_r959010219) for starting point.

There are a few issues:
1. The power toughness values that are picked as it ETBs are only valid on the battlefield it becomes as 0/0 elsewhere. While on the battlefield it is considered as having those values printed on the card for copy effects. Getting this to work properly may require (another) change to how power and toughness are stored. The picked values cannot be stored as the "modified base value" since that will not interact well with effects which further change the base values (e.g. [[Biomass Mutation]]) since the information of what it should be reset to after Biomass Mutation ends will be lost.
2. Same issues with the ability it gains. That ability should be gained by anything that copies it, but this is not consistent.

Start with the Primal Clay implementation and the discussion in pull request 9409, which the issue identifies as the starting point. Trace how its enter-the-battlefield power/toughness values and gained ability are represented, then verify that effects such as Biomass Mutation and copy effects preserve the intended behavior.

Written by the indexing model from the issue text.