fix: register RowDetail and dispose of it only once

[ghiscoding]

The issue was because both the externalResources & extensionList are arrays and to make it easier, they both loop through their arrays when it's time to dispose (destroy) of them. However the RowDetailService was added to both arrays which was disposing of it twice instead of once. This PR fixes this by keeping RowDetail in the extensionList but without adding it to the externalResources array. The other thing to note is that it's better to keep it in extensionList since I already had code in place to get the RowDetail instance from that list as per this Example 21 code

aurelia-slickgrid/packages/demo/src/examples/slickgrid/example19.ts

Lines 43 to 51 in c066730

	get rowDetailInstance() {
	// you can get the SlickGrid RowDetail plugin (addon) instance via 2 ways
	// option 1
	// return this.extensions.rowDetailView.instance || {};
	// OR option 2
	return this.aureliaGrid?.extensionService.getExtensionInstanceByName(ExtensionName.rowDetailView);
	}

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[codecov]

Codecov Report

Attention: Patch coverage is 0% with 2 lines in your changes missing coverage. Please review.

Project coverage is 21.63%. Comparing base (c066730) to head (5039a40).
Report is 1 commits behind head on master.

Files	Patch %	Lines
...slickgrid/src/custom-elements/aurelia-slickgrid.ts	0.00%	2 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##           master    #1253      +/-   ##
==========================================
- Coverage   21.66%   21.63%   -0.02%     
==========================================
  Files           8        8              
  Lines         933      934       +1     
  Branches      323      346      +23     
==========================================
  Hits          202      202              
- Misses        731      732       +1     

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