Factor out common duplicate paths

[djc]

Is your feature request related to a problem? Please describe.

When trying to understand where duplicate dependencies are coming from, the trees displayed by default by cargo deny check are quite helpful. However, in some common cases I think they could be easier to navigate. For example, consider the windows target crates, which are a common source of duplicate dependencies for me:

• windows-sys 0.48 and windows-sys 0.52 each get pulled into the dependency graph
• Each of these depend on respective windows-targets versions (0.48.x and 0.52.x)
• The windows-targets crate then pulls in all of the following:
  • windows_aarch64_gnullvm
  • windows_aarch64_msvc
  • windows_i686_gnu
  • windows_i686_msvc
  • windows_x86_64_gnu
  • windows_x86_64_gnullvm
  • windows_x86_64_msvc

The current output from cargo deny takes... a lot of scrolling to explain this:

https://dpaste.org/rsOoi

(Too long to paste into a GitHub comment.)

Describe the solution you'd like

Would be great to eliminate common subgraphs when explaining duplicate dependencies.