Custom `targetAttributeForScope` breaks target lifecycle callbacks

[koenkivits]

When using a custom targetAttributeForScope callback, target (dis)connected callbacks no longer work. This seems to be because TargetObserver hardcodes the default attribute format:

stimulus/src/core/target_observer.ts

Lines 75 to 77 in 101a060

	private get attributeName() {
	return `data-${this.context.identifier}-target`
	}

All target properties on the controller ([name]Target, has[Name]Target, etc) do work as expected.