Multiline strings should be weighted more towards alignment

[nex3]

Currently this:

testCase._error(
    'Callback ${id}called ($actualCalls) after test case '  
    '${testCase.description} has already been marked as '
    '${testCase.result}.$reason');

is formatted as so:

testCase._error('Callback ${id}called ($actualCalls) after test case '  
    '${testCase.description} has already been marked as '
    '${testCase.result}.$reason');

I like the heuristic of putting an argument on the opening line in general, but I think when it's a continued multiline string it's more important that each line be aligned.

[Hixie]

In #526, the proposed formatting would make the above example format as follows:

testCase._error(
  'Callback ${id}called ($actualCalls) after test case '  
  '${testCase.description} has already been marked as '
  '${testCase.result}.$reason'
);

...which makes it even clearer where the expression starts and ends.

[munificent]

In the forthcoming tall style, this code gets formatted as:

testCase._error(
  'Callback ${id}called ($actualCalls) after test case '  
  '${testCase.description} has already been marked as '
  '${testCase.result}.$reason',
);

All of the strings are aligned, so I think this is done now.