Feat: Add scroll diff decorators

[mkslanc]

Issue #, if available:

Description of changes:

• Improve placement of error decorators (now they would better reflect folds/wraps and lineWidgets)
• Add diff decorators for both inline/split diff views
  
  

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

[codecov]

Codecov Report

Attention: Patch coverage is 96.94323% with 7 lines in your changes missing coverage. Please review.

Project coverage is 87.50%. Comparing base (63add65) to head (91d63c0).

Files with missing lines	Patch %	Lines
src/ext/diff/base_diff_view.js	94.54%	3 Missing ⚠️
src/layer/decorators.js	95.91%	2 Missing ⚠️
src/ext/diff/diff_test.js	98.07%	1 Missing ⚠️
src/ext/diff/scroll_diff_decorator.js	98.52%	1 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##           master    #5807      +/-   ##
==========================================
+ Coverage   87.45%   87.50%   +0.05%     
==========================================
  Files         611      612       +1     
  Lines       45669    45835     +166     
  Branches     7498     7520      +22     
==========================================
+ Hits        39938    40108     +170     
+ Misses       5731     5727       -4     

Flag	Coverage Δ
unittests	87.50% <96.94%> (+0.05%)	⬆️

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