[WIP] [Fix: #11462] Fix over-indentation in Layout/FirstElementHashIndentation

[sambostock]

This investigates fixing #11462. So far, it adds an autocorrection test. I'm still figuring out the details of the autocorrector logic, which I am very much unfamiliar with (cc. @dvandersluis ).

Starting with the example:

def example
  { key1:
    { key2:
      { key3:
	{ key4:
	  { key5:
	    :value
	  }
	}
      }
    }
  }
end

What seems to be happening is that a line break is inserted between { and keyN:. Layout/TrailingWhitespace handles getting rid of the space remaining after {, but everything goes wrong in Layout/FirstHashElementIndentation.

def example
  {
key1:
    {
key2:
      {
key3:
	{
key4:
	  {
key5:
	    :value
	  }
	}
      }
    }
  }
end

It finds key1: in column 0, computes a column delta of 4, which it applies to the key and value lines, even though the value lines don't have the same indentation.

def example
  {
    key1:
        {
    key2:
          {
    key3:
    	{
    key4:
    	  {
    key5:
    	    :value
    	  }
    	}
          }
        }
  }
end

This repeats for key2:, which is not indented as much as it should be relative to its opening {, so the entire thing is indented by the column delta.

def example
  {
    key1:
        {
          key2:
                {
          key3:
          	{
          key4:
          	  {
          key5:
          	    :value
          	  }
          	}
                }
        }
  }
end

This continues to repeat for key3:, key4:, and key5:, respectively:

def example
  {
    key1:
        {
          key2:
                {
                  key3:
                  	{
                  key4:
                  	  {
                  key5:
                  	    :value
                  	  }
                  	}
                }
        }
  }
end

def example
  {
    key1:
        {
          key2:
                {
                  key3:
                  	{
                          key4:
                          	  {
                          key5:
                          	    :value
                          	  }
                  	}
                }
        }
  }
end

def example
  {
    key1:
        {
          key2:
                {
                  key3:
                  	{
                          key4:
                          	  {
                                    key5:
                                    	    :value
                          	  }
                  	}
                }
        }
  }
end

Every level is incorrectly corrected once for each of it's parents, and finally for itself, compounding the error.

Replace this text with a summary of the changes in your PR.
The more detailed you are, the better.

---

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• Squashed related commits together.
• Added tests.
• Ran bundle exec rake default. It executes all tests and runs RuboCop on its own code.
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[dvandersluis]

You should probably just specify (with --only, see line 2666 for an example) which cops you want to run for this test, and then you wouldn't need to explicitly enable/disable cops in the yaml file. It should work fine without explicitly creating a .rubocop.yml file.

Otherwise, test looks alright to me!