Script element layout should be aware of junctions

Summary

This does not work, but it should:

kind: script

build-depends:
- junction.bst:foo.bst
- foo.bst

config:
  layout:
  - element: junction.bst:foo.bst
    destination: / 
  - element: foo.bst
    destination: /sysroot

What is the current bug behavior?

script element at a.bst [line 1 column 0]: script element at a.bst [line 1 column 0]: 'junction.bst:foo.bst' in layout not found in dependencies

What is the expected correct behavior?

It should correctly build.

Relevant logs and/or screenshots

Possible fixes

Other relevant information

• BuildStream version affected: /milestone %BuildStream_v1.x

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