Identification of unused packs, unused components, implicit resolution of trivial component dependencies

[jkrech]

Describe The Problem To Be Solved
a) a CMSIS solution project may list packs unnecessarily as there is no layer, component, generator, device nor board information referenced from it. I.e. any pack listed in csolution/cproject/clayer which is not listed anywhere in any <context>.cbuild.yml should be reported as unused.
b) a project may select components that are not actually used, e.g. as a residual from previously existing component dependencies.
c) when maintaining the CMSIS project yaml files manually it would be convenient if trivial component dependencies are resolved implicitly.

Definition:
"User selected component": a component that was intentionally added by the user
"Trivial dependency resolution": a dependency that can be resolved only by a single component
"User selected dependency resolution": a dependency that can be resolved by more than on component and requires a selection by the user.

Note:
Static code analysis tracking the header file dependency chains could be a method to identify unused components

Annotating components whether they are user selected or resulting from a dependency or being implicitly resolved is an alternative approach. Adding a subnode is noisy but backward compatible.

Implicitly resolving trivial components without storing them in the YAML input is breaking compatibility with previous tool versions.