Http Class Name Cleanup

[alzimmermsft]

This PR standardizes the naming conventions used by our HttpClient implementations, most importantly it standardizes the SPI implementation name which has recently been moved into the public API.

[alzimmermsft]

@JonathanGiles, @srnagar could you review the name changes as this should be merged before shipping azure-core again.

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[alzimmermsft]

/azp run java - core - ci

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Azure Pipelines successfully started running 1 pipeline(s).

[JonathanGiles]

Not a huge fan of how many Utility classes we have - can this be made into, e.g. NettyUtility or similar

[alzimmermsft]

/check-enforcer override

[alzimmermsft]

The CI checks from the manually triggered run passed

https://dev.azure.com/azure-sdk/public/_build/results?buildId=715867&view=results