Problem/Motivation
from @greg.1.anderson on #3091418: Update composer dependencies on 9.0.x following PHP 7.2 requirement.
When we are bumping the Composer dependencies for a major Drupal version release, perhaps we should also make a policy that we increase all of the version constraints for all components listed explicitly in core/composer.json to whatever minimum version they happen to resolve to in composer.lock at that time. Folks will already be adjusting their code to work with the new version of Drupal; it seems like the need for supporting anything older than what is in composer.lock would therefore be minimal. While this is not required, doing this reduces the number of versions of dependencies supported by Drupal, and reduces the number of valid versions of dependencies that are potential solutions from the Composer resolver. (This does not help the current default algorithm, which tries all permutations, but we already have some Composer plugins which optimize this, and such a reduction might help future versions of these do even better.)