Another prototype for async HttpClient APIs

[alzimmermsft]

Description

Related to #45816

This is another prototype for an async HttpClient send method. This design has the async API declared in HttpClient as sendAsync with a default implementation.

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• The pull request does not introduce [breaking changes]
• CHANGELOG is updated for new features, bug fixes or other significant changes.
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Testing Guidelines

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[github-actions]

API Change Check

APIView identified API level changes in this PR and created the following API reviews

io.clientcore:core

[JonathanGiles]

looking good - a few minor comments and some cleanup.

[JonathanGiles]

I'm not convinced we want to default to a bad implementation? If we can do anything useful, it's probably better to do nothing at all?

Suggested change

	* The default implementation doesn't handle challenges. You can override and your implementation as needed.
	* The default implementation doesn't handle challenges. You can override in your implementation as needed.

[alzimmermsft]

I'll leave this question to @g2vinay as I was simply making the async code path based on the sync logic.