Fixes Rails/IndexBy correction when .to_h is separated by a newline

[diogoosorio]

I believe that the test cases included in this commit express well the
problem I'm trying to address, but running the auto-correction against
the following snippet of code:

x.map { |el| [el.to_sym, el] }.
  to_h

Would yield:

x.index_by { |el| el.to_sym }. # notice the ending "dot"

The output isn't parseable/valid Ruby. I belive the problem has to do
with the fact that correction code assumes that the .to_h statement is
always grouped together (which isn't true).

The proposed solution was to compute the trailing characters to be
stripped by subtracting the end position of the map block (the } character)
from end position of the whole expression.

---

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[diogoosorio]

Word of disclosure, this was pretty much the first time I've looked at this codebase (and attempted to understand the AST representation of the code) - it's likely that the approach is incorrect and in that case do "nudge" me in the right direction and I'll re-iterate on the patch (having a core contributor changing the PR directly is also fine by me 👍 ).

[koic]

This approach seems to solve the issue nicely. Thank you for your patch!

[koic]

@diogoosorio RuboCop core's Style/HashTransformKeys and Style/HashTransformValues cops have the same problem. I opened rubocop/rubocop#7903 with you as a co-author. Thank you!