MPR7843: ocamldoc, latex: keep text in {{!lbl} text}

[Octachron]

MPR7843: Currently ocamldoc latex backend translates {{!label}text} to [\ref{label}], discarding the text, if the label points to a (sub)section. Contrarily, the html backend keep the text by translating the ocamldoc markup to <a href=label> text </a>. This PR proposes to keep the text associated to the label in the latex mode too:
{{!label}text} → text[\ref{label}].

[nojb]

Is the lack of space between text and [\ref{label}] intentional?

[Octachron]

This is the format already used for other references, for instance

val x: unit
(**  {{!x}some text} *)

yields
... some text[\ref{val:Module_name.x}]

[nojb]

I see, thanks.

[gasche]

This is a correct fix, thanks!

(Don't forget to add the GPR number in the Changes entry.)

[nojb]

Final dot missing.

[Octachron]

Fixed, thanks!