ext-bcmath and/or ext-gmp are used by MediaWiki in various situations, but their requirement isn't enforced at runtime unless their usage is actually needed (e.g.ScrambleMapping, GlobalIdGenerator on 32 bit machines).
https://gerrit.wikimedia.org/r/990340 at least mentions them in in suggest, but it feels like we should just make them (both?) required extensions. Or at least ext-gmp, which seems to be generally preferred over ext-bcmath.
Could we then drop compat paths for bcmath?
Is there any cases/reasons we can't enforce them (going forward; the suggest should be at least backported) being necessary to run/install/update MW?