Timed Tilt Final Cell

A sled rests on a floor plan grid, a list of equal-length strings where . is open and # is blocked. At second 0 it is still, on the open cell start = [row, col].

Each events[i] = [t, d] tilts the floor at second t toward d, one of "U", "D", "L", "R" or "S" (level). Until the next event, the sled moves one cell per second toward d whenever that cell is open and inside the grid, and otherwise stays put. Events are sorted by strictly increasing t.

Return the sled's [row, col] at second end_time. Row 0 is the top.