Provide a way to show what ends up in a compose

Background

I'm trying to remove Perl from org.freedesktop.Platform//1.8

To do that, I need to figure out why it even gets included into it.

Since platform.bst is a compose element, perl.bst could end up in it for a few different reason:

• perl.bst is a build dependency of platform.bst;
• perl.bst is a run dependency of a build dependency of platform.bst;
• perl.bst is a build dependency of a compose element which itself is a build dependency of platform.bst;
• …

A bst command showing a tree of "what gets included in platform.bst" would be a great help.

The way I think it could work is:

1. a new command, something like: bst show --deps=compose platform.bst
2. recursively, for each build dependency of platform.bst : a. if it is a "compose" element, then continue with its its build dependencies; b. if it is not a "compose" element, then continue with its run dependencies;

Task description

• [ ] Action 1
• [ ] Action 2
• [ ] Action 3

Acceptance Criteria