BF: move the BeforeExperiment JS code to come before the first function

[peircej]

This is essential to make sure that it can be used for importing

[coveralls]

Coverage increased (+0.003%) to 46.513% when pulling 72a055a on peircej:hotfix-JSpreExpLoading into 960214e on psychopy:master.

[codecov-io]

Codecov Report

Merging #3289 (72a055a) into master (d8b0963) will increase coverage by 0.00%.
The diff coverage is 100.00%.

@@           Coverage Diff           @@
##           master    #3289   +/-   ##
=======================================
  Coverage   42.68%   42.68%           
=======================================
  Files         261      261           
  Lines       51063    51072    +9     
  Branches     8816     8819    +3     
=======================================
+ Hits        21798    21802    +4     
- Misses      27060    27064    +4     
- Partials     2205     2206    +1     

Impacted Files	Coverage Δ
psychopy/experiment/flow.py	63.06% <ø> (ø)
psychopy/experiment/_experiment.py	52.34% <100.00%> (+0.25%)	⬆️
psychopy/visual/window.py	60.93% <0.00%> (-0.22%)	⬇️
psychopy/monitors/calibTools.py	37.37% <0.00%> (-0.18%)	⬇️
psychopy/visual/backends/pygletbackend.py	51.48% <0.00%> (+0.37%)	⬆️

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