Remove event building duplication & push to GMSL

[devonh]

Removes event building duplication and moves the funcionality into GMSL since all the sub-steps are already there.

[codecov]

Codecov Report

Patch coverage: 58.46% and project coverage change: +0.13 🎉

Comparison is base (94e81cc) 66.62% compared to head (e0d0a4f) 66.76%.

Additional details and impacted files

@@            Coverage Diff             @@
##             main    #3056      +/-   ##
==========================================
+ Coverage   66.62%   66.76%   +0.13%     
==========================================
  Files         495      495              
  Lines       53625    53542      -83     
==========================================
+ Hits        35729    35748      +19     
+ Misses      14257    14184      -73     
+ Partials     3639     3610      -29     

Flag	Coverage Δ
unittests	46.89% <58.46%> (+0.57%)	⬆️

Flags with carried forward coverage won't be shown. Click here to find out more.

Impacted Files	Coverage Δ
roomserver/internal/input/input_missing.go	68.42% <0.00%> (+1.41%)	⬆️
roomserver/internal/perform/perform_upgrade.go	63.55% <0.00%> (+0.26%)	⬆️
setup/mscs/msc2836/msc2836.go	42.71% <0.00%> (ø)
userapi/api/api.go	70.90% <ø> (ø)
federationapi/internal/perform.go	49.33% <33.33%> (-0.42%)	⬇️
roomserver/internal/perform/perform_leave.go	59.41% <42.85%> (-0.59%)	⬇️
roomserver/internal/perform/perform_join.go	82.00% <50.00%> (+3.16%)	⬆️
clientapi/routing/pushrules.go	79.03% <78.94%> (+15.87%)	⬆️
userapi/internal/user_api.go	63.12% <85.71%> (+0.41%)	⬆️
clientapi/routing/createroom.go	64.57% <100.00%> (+0.60%)	⬆️
... and 3 more

... and 19 files with indirect coverage changes

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