Currently there's no way to sort files by file type when importing into Lightroom; I've always thought this is a weakness even though I shoot Raw probably 99 percent of the time.
What I've done is add a "Send to Lightroom" option to the Send To context menu in Windows. So I'll open a folder of files, sort it by file type, select the raw files only, then simply right-click and select "Send to" the "Adobe Photoshop Lightroom" from the context menu. This immediately invokes Lightroom's Import Dialog box and only the raw files show up there.
Another option is to simply user Windows Explorer of Finder to sort the raw files in the folder, select them, and then simply drag them to the Lightoom icon. This will open Lightroom with the raw files placed in the import dialog box. This is especially simple to do if using Windows with Lightroom in the taskbar at the bottom of your screen.
I've been using FastStone, to import images with for many years.
I shoot both jpg and raw, and often use other programs to simple jpg editing.
So I import folders (they are mixed raw, jpg by date) on my disks to Lightroom when I have time to edit.
I can`t find a way to setup Lightroom, to only import raw from folders.