Fix identical link generation prevention for the "Defined in" section (docs)

[wooster0]

Follow-up of #6280.

Preventing duplicates in types.cr doesn't seems to work. See: Float32.
But it works now by preventing them in generator.cr.

[straight-shoota]

Is there an exaplanation why the existing solution doesn't work as expected?

[straight-shoota]

I guess, in the end it doesn't really matter though. The implementation is equivalent as it applies the correct result to Crystal::Doc::Type#location. So, as long as it works, it's fine by me.

[bcardiff]

@r00ster91 same question @straight-shoota asked. Did you debug why the previous code was not preventing duplicates?

[wooster0]

Hmm I guess it's because at the time in the add_location method, the filename and line_number instance variables of the Location aren't yet correctly modified. But they are modified in the relative_location before the any?. For example here's how filename gets modified before the any? iteration:

filename = filename[1..-1] if filename.starts_with? File::SEPARATOR
filename = filename[4..-1] if filename.starts_with? SRC_SEP

And all these modifications of filename and line_number don't happen before the any? iteration in add_location. That's why it didn't work in add_location I think.

[sdogruyol]

Thank you @r00ster91 👍