feat: delegateService function should be exposed

**Type**: <span ionic-type>feat</span>

**Platform**: <span ionic-platform>all</span>  

<span ionic-description>When creating contributing modules for ionic that make use of the current delegateService style. You have to include that function in your project manually as it's not exposed.

I'd like to see this available under the ionic namespace. Or under an ionic.service namespace or similar.

Thoughts?</span>

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