[Java]: Easier support for modifying scopes

[alzimmermsft]

Clear and concise description of the problem

Java generates the following

@useAuth(
  ApiKeyAuth<ApiKeyLocation.header, "api-key"> | OAuth2Auth<[
    {
      type: OAuth2FlowType.implicit,
      authorizationUrl: "https://login.microsoftonline.com/common/oauth2/v2.0/authorize",
      scopes: ["https://search.azure.com/.default"],
    }
  ]>
)

with scopes being a private static final String[] with the scope value in the definition as the only value. For example:

    @Generated
    private static final String[] DEFAULT_SCOPES = new String[] { "https://search.azure.com/.default" };

and later when creating a client

        if (tokenCredential != null) {
            policies.add(new BearerTokenAuthenticationPolicy(tokenCredential, DEFAULT_SCOPES));
        }

For services that require sovereign cloud audience scope support this means writing complicated post-code generation customizations.

Instead, to simplify this, Java could continue to generate DEFAULT_SCOPES but add in a private String[] scopes that defaults to DEFAULT_SCOPES that can be mutated but does expose a method to do so. And if a service needs sovereign cloud support it could add a non-@Generated method that will be retained if partial-update is enabled. For example,

    @Generated
    private static final String[] DEFAULT_SCOPES = new String[] { "https://search.azure.com/.default" };

    @Generated
    private String[] scopes = DEFAULT_SCOPES;

and in client creation

        if (tokenCredential != null) {
            String[] scopeToUse = (scopes == null) ? DEFAULT_SCOPES : scopes;
            policies.add(new BearerTokenAuthenticationPolicy(tokenCredential, scopes));
        }

and if a service needs to add sovereign cloud support it could be as easy as

    /**
     * Sets the Audience to use for authentication with Microsoft Entra ID.
     * <p>
     * The audience is not considered when using a {@link #credential(AzureKeyCredential) shared key}.
     * <p>
     * If {@code audience} is null the public cloud audience will be assumed.
     *
     * @param audience The Audience to use for authentication with Microsoft Entra ID.
     * @return The updated SearchClientBuilder object.
     */
    public SearchClientBuilder audience(SearchAudience audience) {
        if (audience == null) {
            this.scopes = DEFAULT_SCOPES;
        } else {
            this.scopes = new String[] { audience.toString() }; // the string from SearchAudience is the appropriate value for the cloud target
        }
        return this;
    }

Checklist

• Follow our Code of Conduct
• Read the docs.
• Check that there isn't already an issue that request the same feature to avoid creating a duplicate.