Add QFN-16 1.8x2.6mm P0.4mm (STG3692)

This adds a QFN-16 (called QFN16L by ST) used by the STG3692.

This is one of the few parts on the GMM-7550 modules that we don't have a footprint for.

• https://www.st.com/resource/en/datasheet/stg3692.pdf

This is the recommended FP, but the IPC outcome is slightly different:

Thermal pads are chosen as 1x2 for the vias and the paste:

3D fitup with SamacSys model (https://www.st.com/en/switches-and-multiplexers/stg3692.html#cad-resources)

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To add the "QFN16L" extra tag, this needs !1040 (merged) as a pre-requisite.

Generated results: kicad-footprints!3484