Formatting: adjust heredoc/heregex indent

[helixbass]

The relative indent of heredocs/heregexen should be preserved when its first line ends up indented differently than in the original source

Eg this:

a =
  '''
    b
  '''

gets formatted like:

a = '''
    b
  '''

but should get formatted like:

a = '''
  b
'''

Similarly with eg

a =
  ///
    b
  ///

I don't think this is currently breaking anything semantically, but would be much nicer if it adjusted