[FEATURE REQ] azure-core-v2 for mgmt SDK

# Gaps
## azure-core-management-v2
1. [Resource](https://github.com/Azure/azure-sdk-for-java/blob/8ddf6da837a50543dfcb689887fdd6b1dcf0f8cf/sdk/core/azure-core-management/src/main/java/com/azure/core/management/Resource.java#L18)/[ProxyResource](https://github.com/Azure/azure-sdk-for-java/blob/8ddf6da837a50543dfcb689887fdd6b1dcf0f8cf/sdk/core/azure-core-management/src/main/java/com/azure/core/management/ProxyResource.java#L18)/[ManagementError](https://github.com/Azure/azure-sdk-for-java/blob/8ddf6da837a50543dfcb689887fdd6b1dcf0f8cf/sdk/core/azure-core-management/src/main/java/com/azure/core/management/exception/ManagementError.java#L20)
They are parent classes for resource and management errors. Do we still need them in the new v2?
Their properties are shadowed in child classes anyway for azure-json deserialization.
Another use case be type restriction for premium interfaces. Do we need premium interfaces/libs anymore? How about azure-resourcemanager-authorization and azure-resourcemanager-resources?
Guess we could leave these classes out before conclusions are made. Read-only properties are shadowed, and writable properties can be moved upwards to parent classes, which hopefully won't cause breaking changes.
2. [SystemData](https://github.com/Azure/azure-sdk-for-java/blob/8ddf6da837a50543dfcb689887fdd6b1dcf0f8cf/sdk/core/azure-core-management/src/main/java/com/azure/core/management/exception/ManagementError.java#L20)/[AdditionalInfo](https://github.com/Azure/azure-sdk-for-java/blob/8ddf6da837a50543dfcb689887fdd6b1dcf0f8cf/sdk/core/azure-core-management/src/main/java/com/azure/core/management/exception/AdditionalInfo.java#L20)/etc
They are common properties for resources and management errors. We probably still need them to avoid unnecessary additional classes.
3. LRO related. `PollerFactory`, `SyncPoller`, etc.
4. `AzureEnvironment`(`AzureCloud` endpoint mapping), `AzureProfile`, etc.
5. (02/20/2025) Introduce new ManagedIdentity classes

## azure-core-v2
1. No [`@Headers`](https://github.com/XiaofeiCao/typespec/blob/015aadac79e4d1e1c6a0159b924e8846e5e60bd5/packages/http-client-java/generator/http-client-generator-test/src/main/java/tsptest/armstreamstyleserialization/implementation/FishesClientImpl.java#L74) for setting Content-Type for `GET` methods. Does that mean we need to add header parameter in proxy method?
2. ~~`AzureCloud`~~ fixed by https://github.com/Azure/azure-sdk-for-java/pull/44301
3. TokenCredential and BearerTokenAuthenticationPolicy. issue: https://github.com/microsoft/typespec/issues/5910
4. ~~LRO related: `@ServiceMethod(returns = ReturnType.LONG_RUNNING_OPERATION)`~~ fixed by https://github.com/Azure/azure-sdk-for-java/pull/44670
5. Model `Azure-AsyncOperation` response body. See [Azure-AsyncOperation Resource format](https://github.com/cloud-and-ai-microsoft/resource-provider-contract/blob/master/v1.0/async-api-reference.md#azure-asyncoperation-resource-format).

## codegen
1. Generate only sync-stack methods(asked Sandeep to contact customer when there's beta release for core-v2).
2. Use `ClassType` instead of Class imports in codegen: https://github.com/microsoft/typespec/blob/9f41c06bf265fd0e0a7cde241cf57d4944355252/packages/http-client-java/generator/http-client-generator-mgmt/src/main/java/com/microsoft/typespec/http/client/generator/mgmt/template/FluentManagerTemplate.java#L91
3. Seems now there's no proxy/client methods with `Context` override. Need to generate them. (02/20/2025, use `RequestContext` instead)
4. New class mapping: a. SimpleResponse -> Response
b. CoreUtils (02/20/2025 No CoreUtils anymore, use direct implementation instead)
5. TokenCredential
6. No strongly typed header Response as `ResponseBase`. https://github.com/Azure/azure-sdk-for-java/issues/42640
7. Model `Azure-AsyncOperation` response body, and return `SyncPoller` for POST operations or operations with only `Azure-AsyncOperation` header.

## Premium libraries migration
If we still provide premium libraries support, for backward compatibility, we need to investigate on the migration effort. This will probably take months.
### 1. Resource creation dependency graph
Previously we use `TaskGroup` for resource creation dependencies. E.g. create Network/Storage before creating VM.
Concurrent task execution uses Reactor model. If we support only sync-stack, we either do
1. For simplicity, remove `TaskGroup` and execute in a sequential fashion. Though this will hurt performance.
2. Rewrite task execution using new thread model. We have some edge cases, and need to investigate on the effort.