Adding uparrow as a predefined marker and creating unfilled markershapes

[leckerbeon]

Description

Adds :uparrow as a predefined markershape and causes markercolor=nothing to create an unfilled open shape as requested in #4962.
The changes also make it possible to create unfilled markers of every predefined markershape and also add an :downarrow shape.
Unfortunately I couldn´t quite figure out how to make sticks flip the marker shape vertically if the data value is less or equal to 0.0.

Attribution

• I am listed in .zenodo.json (see How to get acknowledged #3503)

Things to consider

• Does it work on log scales?
• Does it work in layouts?
• Does it work in recipes?
• Does it work with multiple series in one call?
• PR includes or updates tests?
• PR includes or updates documentation?

[codecov]

Codecov Report

Attention: Patch coverage is 60.00000% with 2 lines in your changes missing coverage. Please review.

Project coverage is 86.54%. Comparing base (19e3073) to head (8d09597).
Report is 1 commits behind head on v2.

Files with missing lines	Patch %	Lines
PlotsBase/src/Shapes.jl	0.00%	1 Missing ⚠️
PlotsBase/src/recipes.jl	66.66%	1 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##               v2    #4977      +/-   ##
==========================================
+ Coverage   85.01%   86.54%   +1.53%     
==========================================
  Files          51       51              
  Lines        5985     5991       +6     
==========================================
+ Hits         5088     5185      +97     
+ Misses        897      806      -91     

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