[BUG] PowerShell Core fails to load Azure.Core because of version dependency

[erich-wang]

Describe the bug
Azure.Core should depend on System.Diagnostics.DiagnosticSource nuget package 4.5.1 instead of 4.6 to make it work in PowerShell Core.

PowerShell Core 6.2.2 (released this July) has dependency on version 4.0.3.1 of System.Diagnostics.DiagnosticSource, however Azure.Core depends on higher version 4.0.4.0. PowerShell Core will automatically load 4.0.3.1 of System.Diagnostics.DiagnosticSource when starting, later when loading modules depending on Azure.Core, PowerShell Core will report failure because it need higher version 4.0.4.0 of System.Diagnostics.DiagnosticSource.

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[pakrym]

Downgrading the dependency is a breaking change and we need 4.6 to function properly.

This would be fixed by PowerShell core 7 shipping with updated dependencies: https://github.com/PowerShell/PowerShell/releases/tag/v7.0.0-preview.5

[pakrym]

There is also System.Runtime.CompilerServices.Unsafe pinned by powershell that Azure libraries use it can't not be lowered or removed because we use system.text.json for serialization.