fixup! Re-implement navigate-by-line cursor movement
fixup! Re-implement navigate-by-line cursor movement
fixup! Re-implement navigate-to-line-boundary cursor movement
fixup! Re-implement navigate-by-line cursor movement
fixup! Re-implement navigate-to-line-boundary cursor movement
fixup! Re-implement navigate-by-line cursor movement
fixup! Re-implement navigate-to-line-boundary cursor movement
fixup! Re-implement navigate-to-line-boundary cursor movement
Rename stateful step filters to "scanners"

A scanner (from lexical scanner) is a stateful object that "scans" a
sequence of input steps searching for a step matching a particular
filter (e.g., a line wrap point).