script: Disallow silent bool -> CScript conversion

Summary:

Makes nonsensical stuff like ScriptToAsmStr(false,false); a compile failure

This is a backport of Core PR18621

Test Plan: ninja all check-all

Reviewers: #bitcoin_abc, majcosta

Reviewed By: #bitcoin_abc, majcosta

Differential Revision: https://reviews.bitcoinabc.org/D8935