DomainSourceRouteMatcher caches the domain route key once per process, so cron writes other domains' resolved paths under the wrong domain (3.x backport)

Backport of !461 (merged) to 3.x.

The unit test keeps 3.x's eight argument RouteProvider constructor, its createMock() usage and its annotation style; everything else is the same change.

Unit tests run locally on core 11.3. 3.x requires ^10.2 || ^11, so the core 12 runner used for the 4.x MR does not apply here and the functional coverage goes to CI.