[mono][ios] Drop marshal-ilgen from iOS builds if it is not needed (#88903)

[mono][ios] Drop marshal-ilgen from iOS builds if it is not needed (#88903)

* MarshallingPInvokeScanner is applied to Apple toolchains.

* HelloiOS example uses simpler string marshaling.

* Removing marshal-ilgen from HelloWorld.

* Runtime components and runtime library paths are now decided in the correct order relative to building the native runtime.

* RuntimeComponents is manipulated through an ItemGroup.

* Cleaned up commented old code.

* Reordered runtime components section.

* Addressed more feedback.