Add PHPStan architecture test for `JsonSchemaPropsComponentSourceBase` to detect architecture violations
#3548297+ brought a sane name.
Now let's document the current architecture, including all its warts, to help:
1. ensure it doesn't accidentally become more complex unnecessarily
2. make the parent issue (#3520484+) get `ComponentSourceInterface` to a sufficiently solid state that it can become a public API
task