AE2 Wireless Terminals: Pick-Block Backport

This is a tiny, pure backport of AE2WTLib's "middle-click to pick block" functionality, to v1.20.4, for NeoTech and similar modpacks from the era.

This only applies code already written by upstream (specifically, the backport for v1.20.1 did the hard work.)

I'm using it in my own saves; but it's primarily AI-written; use with a grain of salt. (I'm an experienced dev, and I did put in the effort to ensure this has a minimum of quality, though.)