debugdiscovery: move various computation earlier We are about to add more data to debug discovery (eg: data bout the initial undecided set, number of roundtrip, etc). So we start by cleaning up the code by spliting some computation and some display related preparation. Differential Revision: https://phab.mercurial-scm.org/D9524

debugdiscovery: clarify internal key name in debugobsolete They were probably clear when they got added initially but with more key around, they gain to be clearer. Differential Revision: https://phab.mercurial-scm.org/D9528