actually close audio context when disposing it

[marcelblum]

trafficstars

When looking into #1037 I found that, contrary to the docs, calling context.dispose() does not really close the audio context. Looks like just an oversight. This fixes the following bug:

Tone.getContext().dispose();
// ...
console.log(Tone.getContext().state); // "running", expected "closed"

[codecov[bot]]

Codecov Report

Merging #1041 (a8ac712) into dev (1bedd96) will increase coverage by 0.01%. The diff coverage is 100.00%.

@@            Coverage Diff             @@
##              dev    #1041      +/-   ##
==========================================
+ Coverage   98.44%   98.46%   +0.01%     
==========================================
  Files         184      184              
  Lines        7712     7715       +3     
  Branches      678      678              
==========================================
+ Hits         7592     7596       +4     
  Misses         34       34              
+ Partials       86       85       -1     

Impacted Files	Coverage Δ
Tone/core/context/Context.ts	98.03% <100.00%> (+0.71%)	:arrow_up:

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[marcelblum]

oops just noticed this causes some test fails, will look into soon

[marcelblum]

this should do the trick and also ensure no existing code is broken by this change in case any users were already directly calling context.close() immediately after context.dispose() before the async close process resolves

[tambien]

Thank you @marcelblum for this PR and for all your help in the repo in general! very much appreciated.