Previously the width was set to the width of a single character which
caused issues if the char width was currently zero and since the hidden
input no longer has padding or border the width of the input would end
up being zero which would prevent it from gaining focus.
Having the opacity previously on the .gutter class was making
the gutter background color for the current line be different
than the editor background color.
This removes the need to compute the width of the gutter based
on the line count in the editor and also removes the need to
set the scroll view's left position manually.
