refactor(core): use # instead __ as internal handler prefix

[JKRhb]

In the context of #1097, I remembered that JavaScript nowadays has a built-in prefix for private methods and class fields (#).

As it turns out, fields with this prefix get ignored when calling JSON.stringify, so using it instead of __ for the internal handler maps of the ExposedThing class enables us to get rid of some checks during serialization, which should make the code a bit more idiomatic and slightly increase its performance.

As the handler maps are now truly private, I had adjust some of the test code for it to still work. However, I think the code in question was rather trivial, so this change should hopefully be fine.

[codecov]

Codecov Report

Attention: 12 lines in your changes are missing coverage. Please review.

Comparison is base (49ad831) 75.52% compared to head (2db8506) 75.54%.
Report is 1 commits behind head on master.

Additional details and impacted files

@@            Coverage Diff             @@
##           master    #1104      +/-   ##
==========================================
+ Coverage   75.52%   75.54%   +0.01%     
==========================================
  Files          80       80              
  Lines       16153    16164      +11     
  Branches     1520     1513       -7     
==========================================
+ Hits        12200    12211      +11     
  Misses       3914     3914              
  Partials       39       39              

Files	Coverage Δ
packages/core/src/exposed-thing.ts	67.68% <82.35%> (+0.52%)	⬆️

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[relu91]

PR looks good. I would say that those fields could be better modeled as protected (hence the private modifier would not work), but let's see if we find a use case for extending the exposed-thing in the future.

[danielpeintner]

LGTM and thanks @JKRhb

I just added the comment that it might make sense to put a statements why the # prefix has been used for the internal handlers..