Adding drag meta

[rorticus]

Type: feature

The following has been addressed in the PR:

• There is a related issue
• All code has been formatted with prettier as per the readme code style guidelines
• Unit or Functional tests are included in the PR

Description:

Converting Drag meta to drag middleware. This is basically a direct port of the drag meta. I tried a few ways to be clever but having a single copy of the event listeners, like this has, seemed like a better way to go.

Resolves #514

[agubler]

@rorticus Do you think we should be using a class in the functional middleware? Could this not be done all within the middleware?

[rorticus]

@agubler I can poke around with that some more if you like. I originally went that direction but ran into issues because I wanted a single global event listener, and the middleware is created for each widget. I can take another shot at that though, basically moving a lot of the class stuff up to the module scope?

[codecov]

Codecov Report

Merging #545 into master will increase coverage by 0.02%.
The diff coverage is 98.47%.

@@            Coverage Diff             @@
##           master     #545      +/-   ##
==========================================
+ Coverage   97.43%   97.45%   +0.02%     
==========================================
  Files         117      118       +1     
  Lines        6513     6614     +101     
  Branches     1479     1490      +11     
==========================================
+ Hits         6346     6446     +100     
- Misses        167      168       +1     

Impacted Files	Coverage Δ
src/testing/mocks/middleware/icache.ts	92.85% <92.85%> (ø)
src/core/middleware/drag.ts	99.00% <99.00%> (ø)
src/core/WidgetBase.ts	100.00% <100.00%> (ø)
src/core/middleware/focus.ts	100.00% <100.00%> (ø)
src/core/middleware/icache.ts	100.00% <100.00%> (ø)
src/core/vdom.ts	98.92% <100.00%> (ø)
src/routing/ActiveLink.ts	100.00% <100.00%> (ø)
src/routing/Router.ts	100.00% <100.00%> (ø)
... and 4 more

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