Investigate Azure.Core approaches for handling generation of client-request-id headers

[christothes]

Related to #37427

Given the proposal to have generated REST request creation methods add the client request id header (with the actual header name defined by the API spec), investigate the implications of this in the following scenarios:

• The ClientRequestIdPolicy continues to exist and add the standard client-request-id header

  • Generated code adds a non-standard request id header that does not conflict with the standard header name
  • Generated code adds a non-standard request id header that does conflict with the standard header name

• The ClientRequestIdPolicy goes away and all request id headers are generated

  • Verify CreateClientRequestIdScope still works
  • Determine if there are any other issues

[christothes]

Discussed in stand-up today that, ideally, we would get away from the CreateClientRequestIdScope functionality in favor of a RequstContent option to control this for protocol method clients. The existing policy and CreateClientRequestIdScope would remain for current/legacy clients.