feat(au-compose): ability to compose string as element name

[bigopon]

📖 Description

Adds the ability to understand string as element name to <au-compose/>, it'll throw in case of the name doesn't result in a registered element. All the following usages of <au-compose> will yield the same result:

<au-compose component.bind="el" style="width: 20%;" v="aurelia"></au-compose>
<au-compose component="my-el" style="width: 20%;" v="aurelia"></au-compose>

For component classes:

class MyApp {
  el = MyEl
}

class MyEl {
  @bindable v
}

just as the direct usage of <my-el>:

<my-el style="width: 20%;" v="aurelia"></my-el>

• When composing directly with a custom element constructor, the constructor does not need to be a dependency of the element that owns <au-compose>
• When composing with a custom element name, there must be either a locally or globally registered a custom element with the same name

Closes #1806

cc @fkleuver @Sayan751 @ekzobrain

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 88.37%. Comparing base (3c74be9) to head (a8c622c).
Report is 7 commits behind head on master.

Additional details and impacted files

@@            Coverage Diff             @@
##           master    #1913      +/-   ##
==========================================
- Coverage   88.37%   88.37%   -0.01%     
==========================================
  Files         260      260              
  Lines       22856    22847       -9     
  Branches     5299     5300       +1     
==========================================
- Hits        20198    20190       -8     
+ Misses       2658     2657       -1     

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