Fix registerTex() to handle tex.packages that is already an array

[dpvc]

This PR fixes the component utility that marks preloaded TeX packages so that it will properly merge the new packages into the existing package list if the old list was an array (rather than {'[+]': [...]}).

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 86.71%. Comparing base (e68c42f) to head (c2675cf).
⚠️ Report is 6 commits behind head on develop.

Additional details and impacted files

@@           Coverage Diff            @@
##           develop    #1323   +/-   ##
========================================
  Coverage    86.71%   86.71%           
========================================
  Files          337      337           
  Lines        84074    84077    +3     
  Branches      4758     4758           
========================================
+ Hits         72904    72907    +3     
+ Misses       11170    11147   -23     
- Partials         0       23   +23     

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[zorkow]

lgtm.