Add compose keys for French Bépo keyboard layout

In April 2019, AFNOR, the French normalization organization, published the NF Z71-300 norm to promote two ergonomic keyboard layouts for the French language. AFNOR released a press report (in French) presenting the new norm here. The first proposed layout is an update to the de facto standard AZERTY keyboard, and was already integrated to xkeyboard-config in a previous merge request.

The second layout is a new version of the Bépo keyboard layout, for which an older version is already available in xkb. AFNOR normalized the 1.1 version of this norm, and to this day, its last iteration is the 1.1rc2 version. The details of this layout and its changes from the 1.0 Bépo layout are presented here.

This merge request adds a new default Compose definition file for the fr_FR.UTF-8 locale to add support for the new dead keys introduced in Bépo 1.1 (extended latin, scientific, exponents and indices). This complements the inclusion of the new Bépo 1.1 layout proposed for merging in xkeyboard-config.

Caveat: I do not know if and how these new Compose definitions might impact the standard AZERTY French keyboard. More testing is needed to make sure that this does not lead to any regression for French users not using Bépo. If this turns out to be problematic, this merge request can be discarded, and the charge will be left to Bépo users to edit their ~/.XCompose to be able to use the non-standard dead keys.