refactor(yaml): cleanup composeNode() statements

[timreichen]

Dependent on #6904

This PR refactors composeNode() by using early returns. Some lines code are repeated in order to do that, which can be abstracted further in future PRs.

[codecov]

Codecov Report

❌ Patch coverage is 77.35849% with 12 lines in your changes missing coverage. Please review.
✅ Project coverage is 94.14%. Comparing base (c9ba826) to head (c7083e7).
⚠️ Report is 3 commits behind head on main.

Files with missing lines	Patch %	Lines
yaml/_loader_state.ts	77.35%	12 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##             main    #6905      +/-   ##
==========================================
- Coverage   94.16%   94.14%   -0.03%     
==========================================
  Files         583      583              
  Lines       42811    42825      +14     
  Branches     6815     6821       +6     
==========================================
+ Hits        40314    40316       +2     
- Misses       2446     2457      +11     
- Partials       51       52       +1     

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[kt3k]

Looks easier to understand now. Thanks!