perf: Speed up JSON size calculation

[FrederikBolding]

Alters getJsonSizeUnsafe to not use TextEncoder as this has proven slow on mobile. We don't need full byte length accuracy for the uses of getJsonSizeUnsafe anyway, so this is an OK tradeoff for performance.

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 98.03%. Comparing base (b8792af) to head (e1b9432).
Report is 1 commits behind head on main.

Additional details and impacted files

@@           Coverage Diff           @@
##             main    #3348   +/-   ##
=======================================
  Coverage   98.03%   98.03%           
=======================================
  Files         402      402           
  Lines       11112    11112           
  Branches     1754     1754           
=======================================
  Hits        10894    10894           
  Misses        218      218           

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[Veeezo]

Okay