List transitive platform dependencies changes

[IonBazan]

Currently platform requirement changes are only listed when they are explicitly defined in the root package composer.json. Requiring a package with a transitive platform requirement causes such dependency to be ignored.

That's because such package only appears in packages.<package-name>.require section and not in platform section.

[IonBazan]

One of the challenges here is resolving the common version constraint when multiple packages require same extension/php but in different version or contain multiple constraints.