Add a lock cs_desc_man for DescriptorScriptPubKeyMan

Summary:
Backport of Core PR16528 [7/43] : https://github.com/bitcoin/bitcoin/pull/16528/commits/d8132669e10c1db9ae0c2ea0d3f822d7d2f01345

Depends on D8400

Test Plan:

ninja all check-all

Reviewers: #bitcoin_abc, majcosta

Reviewed By: #bitcoin_abc, majcosta

Differential Revision: https://reviews.bitcoinabc.org/D8405