[policy] limit package sizes

Summary:
Maximum number of transactions allowed in a package is 25, equal to the
default mempool descendant limit: if a package has more transactions
than this, either it would fail default mempool descendant limit or the
transactions don't all have a dependency relationship (but then they
shouldn't be in a package together). Same rationale for 101KvB virtual
size package limit.

Note that these policies are only used in test accepts so far.

This is a backport of core#20833 [8/13] and core#22084 [1/4]
https://github.com/bitcoin/bitcoin/pull/20833/commits/ae8e6df709ff3d52b8e9918e09cacb64f83ae379
https://github.com/bitcoin/bitcoin/pull/22084/commits/6c5f19d9c4d267c54f4dbc4f9d65370ff1e0625b

Depends on D12123

Test Plan: ninja all check-all

Reviewers: #bitcoin_abc, Fabien

Reviewed By: #bitcoin_abc, Fabien

Differential Revision: https://reviews.bitcoinabc.org/D12124