Computes a new cursor position from an old position and a count of positions to move visually.
direction is positive, then the new strong cursor position will be one position to the right of the old cursor position. If
direction is negative, then the new strong cursor position will be one position to the left of the old cursor position.
In the presence of bidirectional text, the correspondence between logical and visual order will depend on the direction of the current run, and there may be jumps when the cursor is moved off of the end of a run.
Motion here is in cursor positions, not in characters, so a single call to move_cursor_visually may move the cursor over multiple characters when multiple characters combine to form a single grapheme.
whether the moving cursor is the strong cursor or the weak cursor. The strong cursor is the cursor corresponding to text insertion in the base direction for the layout.
the byte index of the grapheme for the old index
if 0, the cursor was at the leading edge of the grapheme indicated by
direction to move cursor. A negative value indicates motion to the left.
location to store the new cursor byte index. A value of -1 indicates that the cursor has been moved off the beginning of the layout. A value of MAX indicates that the cursor has been moved off the end of the layout.
number of characters to move forward from the location returned for