Element.prototype.scrollBy, scrollTo and scroll were undefined; they only
existed as no-ops on the window object. Scroll-driven infinite-scroll code
therefore threw "scrollBy is not a function", and scrollTop/scrollLeft were
no-op stubs that always read back 0.
Track a per-element scroll offset so scrollTop/scrollLeft round-trip, add the
three methods accepting either (x, y) or a ScrollToOptions object, and fire a
scroll event so listeners that drive lazy loading can advance. There is no
layout engine, so the offset is not clamped to a real overflow maximum.
Register the new methods in the native-function list so their toString stays
masked.
Fixes#429.
Co-authored-by: sycatle <sycatle@users.noreply.github.com>
