The AUv3 gets registered when you use the Finder to launch the standalone app which contains the AUv3 appex bundle (i.e. double-click on the standalone app’s icon in the Finder).
Additionally, it will only register when both the standalone app and the appex bundle is code-signed. The AUv3 appex must have it’s sandbox compatibility enabled (which the Projucer will do for you automatically).
Additionally, on macOS High Sierra, you also need to reboot after this.
Logic Pro X also needs you to re-scan plug-ins and check the USE AUv3 mode checkbox in Logic’s Plug-in manager.