Backends for Frontends Generator

[GenerateBackendsForFrontends] creates a typed BackendsForFrontends<TRequest, TResponse> factory from selector and handler method pairs.

[GenerateBackendsForFrontends(typeof(CommerceClientRequest), typeof(CommerceClientResponse), GatewayName = "commerce-bff")]
public static partial class CommerceBff
{
    [FrontendSelector("mobile")]
    private static bool IsMobile(CommerceClientRequest request) => request.Client == "mobile";

    [FrontendHandler("mobile")]
    private static CommerceClientResponse Mobile(BackendsForFrontendsContext<CommerceClientRequest> ctx)
        => new(ctx.Request.CustomerId, "compact", 2, false);
}

Diagnostics:

• PKBFF001: host type must be partial.
• PKBFF002: selectors and handlers must be paired by frontend name.
• PKBFF003: selector, handler, or fallback signature is invalid.
• PKBFF004: frontend names must be unique.