After success build_all.sh or assemble_library.sh you should find release folder under distrip folder like
D:\Arduino\VidorBitstream-release\distrib\MKRVIDOR4000_peripherals
That contains examples and src folders and library.properties. I think this is folder that you import / copy to arduino library folder.
src folder should have atleast app.tff and signature.h. Other files are used libraries for using FPGA.
In examples folder you find examples of IP block from FPGA.