fix: #3588091 Add procedural .module file with #[LegacyHook] delegators for Drupal 10.6

The OOP hook classes under src/Hook/ use #[Hook] attributes which Drupal 11+ picks up directly through HookCollectorPass. Drupal 10.6 needs the procedural fallback: a .module file with hook_*() functions decorated with #[LegacyHook] that delegate to the OOP class via \Drupal::service().

Without it, Drupal 10.6 silently skips the entity_type_alter swap (and the form_alter, and the disallowed_configurations_alter). This matches the failure mode observed on the OPT_IN_TEST_PREVIOUS_MAJOR CI run: testBlockStorageIsSwappedOnInstall fails because getStorageClass() returns ConfigEntityStorage instead of DomainAwareConfigEntityStorage. The same root cause cascades through testDisablingEntityTypeDropsTheSwap, testLoadOverrideFreeFoldsRegisteredOverrideForActiveDomain, testRereadAfterOverrideSaveReflectsNewValue, and the converter testConfigRegisteredReturnsOverrideMerged.

Mirrors the pattern the parent module uses in domain_config_ui.module.

Closes #3588091