Add csharp client customizations for Subscription mgmt SDK migration

[ArthurMa1978]

• Configure @azure-typespec/http-client-csharp-mgmt emitter with namespace and emitter-output-dir.
• Rename models, enums, and resources via @@clientName for the C# scope to preserve GA SDK class names from the previous AutoRest mapping.
• Move list operations whose generated rest method names collide with the matching GET into separate client groups via @@clientLocation.
• Avoid namespace conflict when the back-compatible.tsp client name 'Subscription' matches the package's last namespace segment by retargeting these operations to a 'SubscriptionAction' client for the C# scope.
• Map acceptOwnershipUrl/createdTime to acceptOwnershipUri (Uri) and createdOn (utcDateTime) for the C# scope to preserve GA property names and types.

SDK configuration pull request

Purpose of this PR

• Make changes to the SDK configuration only when there are no modifications to the API specification, eliminating the need for an ARM or Stewardship Board API review.

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and followed the instructions by checking all the boxes:

• I confirm this PR is modifying only SDK configurations, and not API related specifications.
• I have reviewed and used the respective tspconfig.yaml templates:
  • ARM tspconfig template
  • Data plane tspconfig template

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[github-actions]

Next Steps to Merge

Next steps that must be taken to merge this PR:

• ❌ This PR targets either the main branch of the public specs repo or the RPSaaSMaster branch of the private specs repo. These branches are not intended for iterative development. Therefore, you must acknowledge you understand that after this PR is merged, the APIs are considered shipped to Azure customers. Any further attempts at in-place modifications to the APIs will be subject to Azure's versioning and breaking change policies. Additionally, for control plane APIs, you must acknowledge that you are following all the best practices documented by ARM at aka.ms/armapibestpractices. If you do intend to release the APIs to your customers by merging this PR, add the PublishToCustomers label to your PR in acknowledgement of the above. Otherwise, retarget this PR onto a feature branch, i.e. with prefix release- (see aka.ms/azsdk/api-versions#release--branches).
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[github-actions]

API Change Check

APIView identified API level changes in this PR and created the following API reviews

Language	API Review for Package
TypeSpec	Microsoft.Subscription
Python	azure-mgmt-subscription
Java	com.azure.resourcemanager:azure-resourcemanager-subscription
JavaScript	@azure/arm-subscriptions

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