Move LockDiff from dep into gps

[carolynvs]

• Move LockDiff and related structs.
• Expose gps.DiffLocks(l1, l2) and gps.DiffProjects(p1, p2).
• All the TOML related annotation will remain in dep, using the same rawX pattern that locks use.

[codecov[bot]]

Codecov Report

Merging #213 into master will increase coverage by 0.26%. The diff coverage is 87.91%.

@@            Coverage Diff             @@
##           master     #213      +/-   ##
==========================================
+ Coverage   78.35%   78.62%   +0.26%     
==========================================
  Files          28       29       +1     
  Lines        4020     4169     +149     
==========================================
+ Hits         3150     3278     +128     
- Misses        648      663      +15     
- Partials      222      228       +6

Impacted Files	Coverage Δ
version.go	79.06% <84.61%> (+1.13%)	:arrow_up:
lockdiff.go	88.23% <88.23%> (ø)
pkgtree/pkgtree.go	81.4% <0%> (-3.67%)	:arrow_down:
source_manager.go	90.35% <0%> (ø)	:arrow_up:
bridge.go	75.91% <0%> (ø)	:arrow_up:
lock.go	95.45% <0%> (+6.81%)	:arrow_up:

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[carolynvs]

I've renamed it per your suggestion and added tests for nil/empty locks.

[sdboyer]

Great - in we go! Thanks! 🎉

[carolynvs]

In before reorg! 😁

[sdboyer]

🏁 🏁 🏁