History serialization fix

[mkslanc]

Issue #, if available: #5887

Description of changes:

• Save session with history on unload
• Fix wrong history serialization

By submitting this pull request, I confirm that you can use, modify, copy, and redistribute this contribution, under the terms of your choice.

Pull Request Checklist:

• No backwards incompatible changes were made to Ace's public interface which is defined through the main typings file (ace.d.ts) and its references:
  • https://github.com/ajaxorg/ace/blob/master/ace.d.ts
  • https://github.com/ajaxorg/ace/blob/master/ace-modes.d.ts
  • https://github.com/ajaxorg/ace/blob/master/ace-extensions.d.ts

Open kitchen-sink @ aaa6d3f9f7131e70b36671f5c3352f4f4418e6cf

Open kitchen-sink @ c26348de35cc2417e8da79f92a169c21ee834201

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 87.78%. Comparing base (97015a6) to head (c26348d).
⚠️ Report is 2 commits behind head on master.

Additional details and impacted files

@@           Coverage Diff           @@
##           master    #5920   +/-   ##
=======================================
  Coverage   87.78%   87.78%           
=======================================
  Files         623      623           
  Lines       45912    45931   +19     
  Branches     7646     7646           
=======================================
+ Hits        40302    40321   +19     
  Misses       5610     5610           

Flag	Coverage Δ
unittests	87.78% <100.00%> (+<0.01%)	⬆️

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