Clean up note spacing to 'staff-bar items
Instead of finding the first item with break-align-symbol
set to
'staff-bar
, Note_spacing::get_spacing
now finds the corresponding
BreakAlignGroup
and uses its extent, which is the combined extent of all
items with break-align-symbol
set to 'staff-bar
.
This is much like commit b8860abf and avoids similar problems.