Adds createChildContext method to ComponentDialog

[ltwlf]

Description

Add a createChildContext method ComponentDialog like in the dotnet implementation. There are cases where you need to create the child content from the outside and it makes the code cleaner and less redundant.

Specific Changes

• Adds createChildContext method to ComponentDialog

[coveralls]

Pull Request Test Coverage Report for Build 84766

• 9 of 11 (81.82%) changed or added relevant lines in 1 file are covered.
• No unchanged relevant lines lost coverage.
• Overall coverage increased (+0.03%) to 87.678%

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Changes Missing Coverage	Covered Lines	Changed/Added Lines	%
libraries/botbuilder-dialogs/src/componentDialog.ts	9	11	81.82%

Totals
Change from base Build 84761:	0.03%
Covered Lines:	4912
Relevant Lines:	5389

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💛 - Coveralls

[Stevenic]