Assembly loading improvements

[isra-fel]

Description

• This PR disables assembly preloading because we already implemented lazy-loading.
• The definitions of dependency assemblies are centralized, and with more flexibility. You can specify a range of PowerShell versions to load a certain assembly, or a type of OS. Thanks to this the size of Az module is also reduced.
  • Duplicated Azure.Identity.dll is removed.
  • The following assemblies used to have both netframework and netstandard version in our codebase. This PR removed the netframework versions:
    • Microsoft.Bcl.AsyncInterfaces
    • Microsoft.IdentityModel.Abstractions
    • System.Memory.Data
    • System.Text.Json

Design

The core implementation is a new project named AssemblyLoading (and a new assembly Microsoft.Azure.PowerShell.AssemblyLoading) in Az.Accounts module. The two assembly loaders CustomeAssemblyLoader and AzAssemblyLoadContext will depend on this project to provide the list of assemblies to load according to the environment.

Checklist

• Check this box to confirm: I have read the Submitting Changes section of CONTRIBUTING.md and reviewed the following information:

• SHOULD select appropriate branch. Cmdlets from Autorest.PowerShell should go to generation branch.
• SHOULD make the title of PR clear and informative, and in the present imperative tense.
• SHOULD update ChangeLog.md file(s) appropriately
  • For any service, the ChangeLog.md file can be found at src/{{SERVICE}}/{{SERVICE}}/ChangeLog.md
  • A snippet outlining the change(s) made in the PR should be written under the ## Upcoming Release header in the past tense. Add changelog in description section if PR goes into generation branch.
  • Should not change ChangeLog.md if no new release is required, such as fixing test case only.
• SHOULD have approved design review for the changes in this repository (Microsoft internal only) with following situations
  • Create new module from scratch
  • Create new resource types which are not easy to conform to Azure PowerShell Design Guidelines
  • Create new resource type which name doesn't use module name as prefix
  • Have design question before implementation
• SHOULD regenerate markdown help files if there is cmdlet API change. Instruction
• SHOULD have proper test coverage for changes in pull request.
• SHOULD NOT introduce breaking changes in Az minor release except preview version.
• SHOULD NOT adjust version of module manually in pull request

[isra-fel]

/azp run

[azure-pipelines]

Azure Pipelines successfully started running 3 pipeline(s).

[isra-fel]

Done

todo:

• https://cs.github.com/Azure/azure-powershell/blob/34f9661146728f308b064663bd4f0e94c1794ecc/tools/Tools.Common/Loaders/CmdletLoader.cs?q=repo%3AAzure%2Fazure-powershell+PreloadAssemblies#L45
• https://cs.github.com/Azure/azure-powershell/blob/34f9661146728f308b064663bd4f0e94c1794ecc/src/Storage/Storage/Storage.csproj?q=repo%3AAzure%2Fazure-powershell+PreloadAssemblies#L27
• https://cs.github.com/Azure/azure-powershell/blob/34f9661146728f308b064663bd4f0e94c1794ecc/src/lib/test.net472.config?q=repo%3AAzure%2Fazure-powershell+PreloadAssemblies#L12

[isra-fel]

These lines were added to support data plane track 2 SDK (#11520). They preload Azure.Core.dll and its dependencies. But now Azure.Core is handled by Az.Accounts so these are no longer needed.
cc @blueww