Yes. But this is far far far away from "designers must code." Except for a few unicorns, this just leads to people who are mediocre at both design and code. A designer who is bogged down in code will also produce bad designs, especially when they let their inability to think of how something will be coded (because they aren't advanced coders) limit them!
Designers have their own tool chain to prototype UIs and user interactions, but these are not UI devtools.
I'm not advocating that designers should code -- far from it. I wish they had better tools for modeling user experiences.
You mention that designers have their own toolchains for prototyping, but these has nothing to do with UI dev tools. I've often wondered why this would have to be so.
Look at other advanced design fields like architecture and industrial design. It would be unthinkable today that professional architects would just draw a facade and not use CAD to actually model the structure. Similarly, it would be very unusual for an industrial designer to model a product using a toolchain that is entirely separate from manufacturing. The assumption today is that CAD and CAM work together, not separately.
Why can't we have the same in software? For my part, I've been trying to work on a solution in the form of apps like React Studio [1]. It's not there yet, but I'm convinced that proper software modeling tools will happen eventually.
UI dev tools are tools for producing a UI. Prototyping and modeling tools are quite different; it would be unthinkable today for a professional architect to build the building they are architecting and not actually model the structure. Also consider that much of the design that goes on is far away from the actual pixels that show up on the screen; e.g. interaction designers have very little to do with the UI.
I'll just add one caveat - it's my experience that developers often have little interest in great design code. I write far better mobile design code than any developer I've met (which to be fair isn't many). For me, I contribute best by focusing on that part, leaving developers to focus on their interests which is often new languages, tools, libraries, architecture...
Designers have their own tool chain to prototype UIs and user interactions, but these are not UI devtools.