Adding Edge on Windows 7, 8 and 8.1

[jaydiablo]

Fixes #2390.

Microsoft pushed an update to Windows 7 and 8 this summer that enabled the Chromium Edge browser on those versions of windows: https://betanews.com/2020/06/20/microsoft-edge-windows-7-windows-8/

I pulled some additional UAs from our logs to add test coverage. Also noticed that Headless Edge is available as well, so added that browser with tests: https://headlesstesting.com/blog/edge-headless-testing

[codecov]

Codecov Report

Merging #2393 (c1a8176) into 6.0.x (c46be08) will decrease coverage by 0.00%.
The diff coverage is 36.36%.

@@             Coverage Diff              @@
##              6.0.x    #2393      +/-   ##
============================================
- Coverage     51.78%   51.78%   -0.01%     
  Complexity      899      899              
============================================
  Files          1801     1803       +2     
  Lines         65605    65625      +20     
  Branches      29497    29511      +14     
============================================
+ Hits          33974    33981       +7     
- Misses        31631    31644      +13     

Flag	Coverage Δ	Complexity Δ
full	46.63% <36.36%> (-0.01%)	0.00 <0.00> (ø)
lite	2.14% <36.36%> (+0.01%)	0.00 <0.00> (ø)
standard	26.86% <36.36%> (+<0.01%)	0.00 <0.00> (ø)

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Impacted Files	Coverage Δ	Complexity Δ
...ser-agents/browsers/edge-browser/edge-generic.json	7.14% <0.00%> (-0.41%)	0.00 <0.00> (ø)
...s/browsers/edge-browser/headless-edge-generic.json	0.00% <0.00%> (ø)	0.00 <0.00> (?)
...nts/browsers/edge-browser/headless-edge-76-on.json	57.14% <57.14%> (ø)	0.00 <0.00> (?)
.../user-agents/browsers/edge-browser/edge-76-on.json	100.00% <100.00%> (ø)	0.00 <0.00> (ø)

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