The goal of this function is to apply the DocFragment transformation that is required when
transforming into the final Markdown, which is applying the computed indent to each line in
each doc fragment (a DocFragment can contain multiple lines in case of #[doc = ""]).
Return the doc-comments on this item, grouped by the module they came from.
The module can be different if this is a re-export with added documentation.
Simplified version of the corresponding function in rustdoc.
If the rustdoc version returns a successful result, this function must return the same result.
Otherwise this function may return anything.
Removes excess indentation on comments in order for the Markdown
to be parsed correctly. This is necessary because the convention for
writing documentation is to provide a space between the /// or //! marker
and the doc text, but Markdown is whitespace-sensitive. For example,
a block of text with four-space indentation is parsed as a code block,
so if we didn’t unindent comments, these list items