Format tool removes whitespace from heredoc

[straight-shoota]

The format tool shows an odd and unwanted behaviour with heredocs: In some cases, when the heredoc uses leading whitespace, the formatter removes a single whitespace at the beginning. Multiple runs of the formatter each remove only one whitespace until there is none left. It removes only leading whitespace which is to be ignored, so the meaning of the source code does not change. Nevertheless, the leading whitespace is usually there for a reason (readability) and it is annoying to revert.

Example:

{
  "foo" => <<-END
    bar
    END,
}

Result of crystal tool format:

{
  "foo" => <<-END
   bar
   END,
}

Result of running crystal tool format four times:

{
  "foo" => <<-END
bar
END,
}

I found this to happen only when the heredoc is a value in a hash definition, but there might be other cases, too. The heredoc without the hash will not be altered:

<<-END
    bar
    END,

[straight-shoota]

Could be related to #4000