As per a suggestion by Oliver on the PR thread, maintaining indentation
in the suggested code is futile because of the changes in the compiler
and the messiness of real-world code. rustfmt will do the indentation if
required, so we don't need to do it.
I had my own implementation of what `trim_multiline()` seems to be doing, so
I just started using `trim_multiline()`. Some other functions, like
those block alignment, are general enough to be used elsewhere, so moved
them to utils.
The previous version had troubles computing suggestions without macro expansions
creeping in. This fixes it by using original_sp, which works on AST nodes.
