Custom element resource support

[maier49]

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:
Adds a flag to factory's using the resource middleware

• Uses attributes/properties on the custom element to configure the resource (right now only works if those are not used but does not reserve them)
• Defaults to a memory template and empty data set
• Does not expose createTemplate functions since they only provide typing, instead taking a template directly

Example usage here
Resolves dojo/widgets#1481

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[maier49]

@matt-gadd The prototype now handles everything in the middleware (and has tests). It also occurs to me that with this change to the logic we could also change the type on the resource property to allow passing an object with all the options directly instead of needing a parent that uses the resource middleware to create a resource prop

[codecov]

Codecov Report

Merging #815 into master will increase coverage by 0.00%.
The diff coverage is 100.00%.

@@           Coverage Diff           @@
##           master     #815   +/-   ##
=======================================
  Coverage   97.53%   97.54%           
=======================================
  Files         127      127           
  Lines        7964     7970    +6     
  Branches     1836     1839    +3     
=======================================
+ Hits         7768     7774    +6     
  Misses        196      196           

Impacted Files	Coverage Δ
src/core/middleware/resources.ts	98.58% <100.00%> (+0.01%)	⬆️

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