Fix for #772: help instructions pop-up position with responsive behaviour

[koalyptus]

Description

As described in #772, fix help instructions positioning when responsive behaviour is on and working table element features a horizontal scrollbar. This also adds a help_instructions.container_adjust_left_position setting allowing pop-up positioning pixel adjustments if needed.

Type of change

• [x] Bug fix (non-breaking change which fixes an issue)

Checklist:

• [x] My code follows the style guidelines of this project
• [x] I have performed a self-review of my own code
• [x] I have commented my code, particularly in hard-to-understand areas
• [x] I have made corresponding changes to the documentation
• [x] My changes do not lower current test coverage
• [x] I have added tests that prove my fix is effective or that my feature works
• [x] New and existing unit tests pass locally with my changes

[codecov[bot]]

Codecov Report

Merging #780 into master will increase coverage by 0.03%. The diff coverage is 100.00%.

@@            Coverage Diff             @@
##           master     #780      +/-   ##
==========================================
+ Coverage   89.06%   89.09%   +0.03%     
==========================================
  Files          39       39              
  Lines        4500     4504       +4     
  Branches      325      327       +2     
==========================================
+ Hits         4008     4013       +5     
  Misses        475      475              
+ Partials       17       16       -1     

Impacted Files	Coverage Δ
src/dom.js	84.61% <ø> (ø)
src/modules/help.js	90.62% <100.00%> (+1.49%)	:arrow_up:

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