Review Mozilla 1810641: Enable overscroll on Windows on all channels

Link: https://bugzilla.mozilla.org/show_bug.cgi?id=1810641

@thorin is overscroll something we need to consider re Fingerprinting or is it a case where so-long as everyone has it it's fine. Skimming the ticket suggests the overscroll only happens when scrolling via touch.

EDIT: fwiw enabling the provided pref on Linux did not enable any new functionality on my laptop, but libinput is kind of a shitshow w/ regards to touchpad support/functionality so it may just be seeing it a mouse+scroll wheel.

/cc @donuts