Improve laziness of container XML parsing

[xificurk]

Parsing the XML into the DTOs is a costly operation on large Kernels. This PR defers the ServiceMap and ParameterMap initialization until the first use of their content.

[VincentLanglet]

I think this is a BC break, given the fact that the interface has @api. If someone implements the interface his code will break.

Same exist for ParameterMap ; so I'll need @ondrejmirtes review.

[ondrejmirtes]

Yeah, removing the static keyword is a BC break. For 3.0 we could add @api-do-not-implement there (many PHPStan core interface already have it) and make the interface nicer. But I think this improvement could still be implemented without changing the interfaces?

[xificurk]

@ondrejmirtes Yes, I'll rework this to maintain BC.

Removing the static would make sense for 3.0 - all the existing calls are on a dynamically resolved instance. No true static calls exist and given the implemented logic, they should not exist.

[staabm]

@xificurk please also provide a profiler screenshot / hyperfine perf numbers so we can see the impact of this PR