Issue #3593113 by mably: [3.0.x backport] Multi-config form registration check requires all config names

Backport to 3.0.x of the fix merged to 3.x (MR !390 (merged)).

isConfigurationRegisteredForDomain() now requires every config name in a set to be registered, so a multi-config form (e.g. account settings, which lists system.site first) no longer shows the remove toggler just because a shared config is registered.

The cherry-pick applied cleanly. The only backport-specific change is the kernel test: on 3.0.x the domain_config language_manager decorator inherits the parent service definition (ConfigurableLanguageManager) only when the language module is installed (3.x decoupled this via #3588828), so the test installs language. Verified locally: passes with the fix, fails without.