JQAutocomplete (follow-up to issue #1232): content-type for json call…

[jbrichau]

…back in jQueryUI autocompleter should be application/json and not text/plain. Reworked the callback implementation to no longer create intermediate objects for serialization to json but use the json canvas directly.

[codecov]

Codecov Report

Patch coverage has no change and project coverage change: -0.03 ⚠️

Comparison is base (9866f65) 54.13% compared to head (3d53ed6) 54.11%.

Additional details and impacted files

@@            Coverage Diff             @@
##           master    #1364      +/-   ##
==========================================
- Coverage   54.13%   54.11%   -0.03%     
==========================================
  Files        8870     8871       +1     
  Lines       72018    72049      +31     
==========================================
  Hits        38989    38989              
- Misses      33029    33060      +31     

Impacted Files	Coverage Δ
...eFunctionalTest.class/instance/renderContentOn..st	0.00% <0.00%> (ø)
...est.class/instance/renderSelectedPackageNameOn..st	0.00% <0.00%> (ø)
.../JQAutocomplete.class/instance/search.callback..st	0.00% <0.00%> (ø)
...complete.class/instance/search.labels.callback..st	0.00% <0.00%> (ø)
...e/JQAutocomplete.class/instance/sourceCallback..st	0.00% <0.00%> (ø)

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