[JS] Implement Thread capabilities in JS

[soywiz]

We need to propagate an object between calls to determine in which thread we are.

[codecov[bot]]

Codecov Report

Merging #276 into master will increase coverage by 0.01%. The diff coverage is 53.57%.

@@             Coverage Diff              @@
##             master     #276      +/-   ##
============================================
+ Coverage     17.85%   17.86%   +0.01%     
  Complexity      386      386              
============================================
  Files           314      314              
  Lines         20802    20809       +7     
  Branches       4493     4495       +2     
============================================
+ Hits           3714     3718       +4     
- Misses        16405    16407       +2     
- Partials        683      684       +1

Impacted Files	Coverage Δ	Complexity Δ
...-core/src/com/jtransc/text/JTranscStringTools.java	0% <ø> (ø)	0 <0> (ø)	:arrow_down:
...transc-rt-core/src/com/jtransc/JTranscWrapped.java	0% <ø> (ø)	0 <0> (ø)	:arrow_down:
...nsc-rt-core/src/com/jtransc/io/JTranscConsole.java	0% <ø> (ø)	0 <0> (ø)	:arrow_down:
jtransc-rt-core/src/com/jtransc/JTranscArrays.java	0% <ø> (ø)	0 <0> (ø)	:arrow_down:
...ransc-gen-php/src/com/jtransc/gen/php/PhpTarget.kt	0% <ø> (ø)	0 <0> (ø)	:arrow_down:
...ansc-gen-cs/src/com/jtransc/gen/cs/CSharpTarget.kt	0% <ø> (ø)	0 <0> (ø)	:arrow_down:
...ransc-gen-cpp/src/com/jtransc/gen/cpp/CppTarget.kt	82.03% <ø> (ø)	4 <0> (ø)	:arrow_down:
...sc-gen-dart/src/com.jtransc.gen.dart/DartTarget.kt	91.7% <ø> (ø)	6 <0> (ø)	:arrow_down:
...sc-gen-haxe/src/com/jtransc/gen/haxe/HaxeTarget.kt	80.41% <ø> (ø)	11 <0> (ø)	:arrow_down:
...core/src/com/jtransc/gen/common/CommonGenerator.kt	0% <0%> (ø)	0 <0> (ø)	:arrow_down:
... and 1 more

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