Fixes#1149.
VoiceOver expects AXLineForIndex and AXRangeForLine to be consistent with
the movement by line using arrow up/down. That means it expects "line"
to mean softline.
VoiceOver also distinguishes commands to move by:
* paragraph (hardline): VO-Shift-PgUp/PgDown
* line (softline): VO-up/down
These are available when interacting with the text area (VO-Shift-down).
This commit therefore fixes the AXLineForIndex and AXRangeForLine
to make "line" mean "softline" instead of "hardline" as was the case
until now.