GeneratedClient constructor should not mutate the options bag

[jeremymeng]

my convenience layer code creates two clients using the same options bag:

     const authClient = new GeneratedClient(endpoint, internalPipelineOptions);
     this.client = new GeneratedClient(endpoint, internalPipelineOptions);

It leads to duplicate library infor in user-agent header for the second client because the generated client's constructor updated options.userAgentOptions.userAgentPrefix. I fixed it by

-    options.userAgentOptions = {
-      userAgentPrefix: userAgentPrefix
-    };
-
     const optionsWithDefaults = {
       ...defaults,
       ...options,
+      userAgentOptions: {
+        userAgentPrefix
+      },
       baseUri: options.endpoint || "{url}"
     };

[sarangan12]

Code complete with #1042. Will be included in the next release.