Implement SetupGeneration for DescriptorScriptPubKeyMan

Summary:
Backport of Core PR16528 [20/43] : https://github.com/bitcoin/bitcoin/pull/16528/commits/e014886a342508f7c8d80323eee9a5f314eaf94c

Depends on D8417

Test Plan:

ninja all check-all

Reviewers: #bitcoin_abc, PiRK, majcosta

Reviewed By: #bitcoin_abc, PiRK, majcosta

Differential Revision: https://reviews.bitcoinabc.org/D8418