Add missing preLoaded() call for input/mml when a11y is used.

[dpvc]

The semantic-enrich extension has input/mml as a dependency (so that it can re-parse the SRE output), but it wasn't being listed in the preloaded items when the A11y utilities were being included in a combined component. That means that loading tex-chtml.js, for example, and adding input/mml to the loaded items could cause the extension to be loaded a second time without sharing the common code, leading to problems with objects and options not being properly shared.

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 86.66%. Comparing base (27c47f3) to head (c13e406).

Additional details and impacted files

@@           Coverage Diff            @@
##           develop    #1377   +/-   ##
========================================
  Coverage    86.66%   86.66%           
========================================
  Files          338      338           
  Lines        84384    84384           
  Branches      4779     4779           
========================================
  Hits         73131    73131           
+ Misses       11253    11230   -23     
- Partials         0       23   +23     

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