CB-14141: Don't duplicate resource files in xcodeproj

[dpogue]

Platforms affected

iOS

What does this PR do?

When copying a resource-file to a target that already exists, don't add it to the xcodeproj file a second time.

My particular scenario is that I wanted to overwrite CDVLaunchScreen.storyboard and it was getting added to the xcodeproj twice and causing weird failures.

What testing has been done on this change?

Checklist

• Reported an issue in the JIRA database
• Commit message follows the format
• Added automated test coverage as appropriate for this change.

[codecov-io]

Codecov Report

Merging #373 into master will increase coverage by 0.04%.
The diff coverage is 100%.

@@            Coverage Diff             @@
##           master     #373      +/-   ##
==========================================
+ Coverage   63.99%   64.03%   +0.04%     
==========================================
  Files          14       14              
  Lines        1697     1699       +2     
  Branches      286      287       +1     
==========================================
+ Hits         1086     1088       +2     
  Misses        611      611

Impacted Files	Coverage Δ
bin/templates/scripts/cordova/lib/prepare.js	84.72% <100%> (+0.06%)	⬆️

---

Continue to review full report at Codecov.

Legend - Click here to learn more
Δ = absolute <relative> (impact), ø = not affected, ? = missing data
Powered by Codecov. Last update 46da4bc...e2c885f. Read the comment docs.

[jcesarmobile]

LGTM