Package_DFN_QFN: add TQFN-20-1EP_4x4mm_P0.5mm_EP2.9x2.9mm package

This MR adds a TQFN20 package with a 4x4mm package and a 2.9mm EP.

• datasheet: https://pdfserv.maximintegrated.com/package_dwgs/21-100172.PDF
• generated by: kicad-footprint-generator!716 (merged)