Fix client token credentials issue before Az.Account module is imported.

[vidai-msft]

Description

This PR fixes the exception when pre-initialization was executed while Az.Accounts was not loaded.
The solution was to register necessary component during TestFx initialization.

The PR also refactors the code in WithManagementClients method to remove unnecessary function calls.

Mandatory Checklist

• Please choose the target release of Azure PowerShell. (⚠️Target release is a different concept from API readiness. Please click below links for details.)

  • General release
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  • No need for a release

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

• SHOULD update ChangeLog.md file(s) appropriately
  • For SDK-based development mode, update 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.
  • For autorest-based development mode, include the changelog in the PR description.
  • Should not change ChangeLog.md if no new release is required, such as fixing test case only.
• SHOULD regenerate markdown help files if there is cmdlet API change. Instruction
• SHOULD have proper test coverage for changes in pull request.
• SHOULD NOT adjust version of module manually in pull request

[azure-client-tools-bot-prd]

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[notyashhh]

@vidai-msft Looks Great!!

I couldn't find anything wrong in the code changes. We don't need a changelog update since this does not require a release.
Are there any docs/readmes' that we have to update?

If not, we can get it merged :))

[vidai-msft]

@vidai-msft Looks Great!!

I couldn't find anything wrong in the code changes. We don't need a changelog update since this does not require a release. Are there any docs/readmes' that we have to update?

If not, we can get it merged :))

@notyashhh No docs need update.