fix: respect herecomments when computing function bounds

[alangpierce]

Fixes decaffeinate/decaffeinate#687

Previously, the bounds of a function body were shrunk to only include semantic
tokens, which could cause a block comment to get moved outside the body and be
improperly indented after the normalize step. Now, we include the comments as
part of the body.

This is a small change that gets this case to work, but it might be that in the
future we'll want to avoid all AST location adjustment and/or put block comments
in the AST.

[eventualbuddha]

What happens when a block comment follows a function body but isn't indented to match?

[alangpierce]

I think the block comment is still viewed as outside the function, since the CoffeeScript parser doesn't include it in the function bounds in the first place. This code path that I'm changing is just shrinking the location data from the CoffeeScript parser, but if the CoffeeScript parser got everything correct, I think it wouldn't be necessary.

But I can add a test to double-check.