12V AC to 12V DC converter to power an Arduino and some WS2812B 5050 LEDs
You wouldn't normally convert low voltage AC to DC with a chip.
You would normally use a full wave bridge rectifier followed by a smoothing capacitor.
That combination gives you a smooth(ish) DC voltage.  Given 12VRMS and assuming 0.7V forward voltage for the diodes, you will get about 15V DC.
You can then use whatever buck converter (or linear regulator) you like to convert the 15VDC to 12VDC.

The simplest solution for most hobbyists is to use a commercial 12V supply.  If you have to order parts to make the power supply, you might as well save yourself the hassle of building it and just buy one instead of the parts.
Not to say that building one to learn how they work is a bad idea.  It used to be common for hobbyists to build their own power supplies.  They weren't as commonly and cheaply available as they are today, so it was common to build a power supply as part of the project itself.
That does, of course, take time away from reaching the actual goal of the project.