Stop invoking the module handler in the constructor

Problem/Motivation

Invoking the module handler early, e.g. in the constructor of a service, can have bad side effects: #3207813: ModuleHandler skips all hook implementations when invoked before the module files have been loaded. Also, it's generally recommended to keep constructors as simple as possible when using dependency injection.

Proposed resolution

Inject the module handler into a property and load the dictionary on demand.