[eas-cli] more branch map utility functions

[quinlanj]

Why

extra utility function for branch mapping

Test Plan

• new tests pass

[quinlanj]

/changelog-entry chore more branch map utility functions

[github-actions]

Size Change: +1.72 kB (0%)

Total Size: 42.3 MB

Filename	Size	Change
./packages/eas-cli/dist/eas-linux-x64.tar.gz	42.3 MB	+1.72 kB (0%)

_{compressed-size-action}

[codecov]

Codecov Report

Merging #2001 (6fd7554) into main (e42ea7e) will increase coverage by 0.02%.
Report is 2 commits behind head on main.
The diff coverage is 100.00%.

❗ Current head 6fd7554 differs from pull request most recent head 3d7024d. Consider uploading reports for the commit 3d7024d to get more accurate results

@@            Coverage Diff             @@
##             main    #2001      +/-   ##
==========================================
+ Coverage   53.04%   53.05%   +0.02%     
==========================================
  Files         507      507              
  Lines       18399    18405       +6     
  Branches     3856     3857       +1     
==========================================
+ Hits         9757     9763       +6     
  Misses       7948     7948              
  Partials      694      694              

Files Changed	Coverage Δ
packages/eas-cli/src/rollout/branch-mapping.ts	94.12% <100.00%> (+0.28%)	⬆️

[wschurman]

One naming nit, otherwise looks good.

[github-actions]

✅ Thank you for adding the changelog entry!