Extract XML-related utilities into a separate file

[IndrajeetPatil]

Since the utils.R is getting quite large.

Similar to xp_utils.R.

[MichaelChirico]

I would let this PR simmer a while. There's some cost to understanding git history when moving code between files like this. If there will only ever be two functions in the new utils file, I'm not sure it's worth it.

It might be more fruitful to group some of the other utils together, or to try removing some of them.

[codecov-commenter]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 99.63%. Comparing base (fc2268f) to head (698eb8f).
Report is 3 commits behind head on main.

❗ Current head 698eb8f differs from pull request most recent head b07db9a

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Additional details and impacted files

@@            Coverage Diff             @@
##             main    #2201      +/-   ##
==========================================
+ Coverage   98.15%   99.63%   +1.48%     
==========================================
  Files         125      115      -10     
  Lines        5738     5235     -503     
==========================================
- Hits         5632     5216     -416     
+ Misses        106       19      -87     

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