Merge topic 'vs-depends-dedup'

42bc67bd VS: De-duplicate custom command dependencies
d03a6fc8 VS: Clarify name of custom commands AdditionalInputs variable
fcedf8e5 VS: Isolate custom command input/output generation scopes

Acked-by: Kitware Robot <kwrobot@kitware.com>
Merge-request: !3388