.Net: #5908 conditionalize dependencies

[thompson-tomo]

Motivation and Context

This reduces the dependency graph by making STJ only included on net standard

Description

This simply makes dependencies which are available as part of the framework conditional so that they are not being un-necessarily included

Contribution Checklist

• The code builds clean without any errors or warnings
• The PR follows the SK Contribution Guidelines and the pre-submission formatting script raises no violations
• All unit tests pass, and I have added new tests where possible
• I didn't break anyone 😄

Closes #5908

[WeihanLi]

maybe also Microsoft.BCL.* packages

[markwallace-microsoft]

Should this be in the netstandard2.0 item group?

[thompson-tomo]

U are right will make that additional cleanup tomorrow morning my time.

[thompson-tomo]

@markwallace-microsoft it appears that Microsoft.BCL.HashCode is not needed at all & Microsoft.Bcl.AsyncInterfaces is being imported as a transitive dependency. Not sure if the abstractions explicitly need this dependency.

[markwallace-microsoft]

@dmytrostruk is going to continue this work, tracking with #8109 . We want to make sure we have the correct test coverage before merging this.

[markwallace-microsoft]

@dmytrostruk is going to continue this work, tracking with #8109., this PR will be updated as part of this task