[ refactor ] Coverage: Made BlockingVar into record.
[ comment ] Coverage.split.
[ rename ] splitClauseWithAbs --> splitClauseWithAbsurd
[ refactor ] forM for mapM, var x for Var x [].
[ refactor ] Extracted splitResult from Coverage.cover.
Merge branch 'maint-2.4.0' of github.com:agda/agda into maint-2.4.0