Function insert_outlives_clause 

pub(crate) fn insert_outlives_clause<'tcx>(
    tcx: TyCtxt<'tcx>,
    arg: GenericArg<'tcx>,
    outlived_region: Region<'tcx>,
    span: Span,
    required_clauses: &mut FxIndexMap<ArgOutlivesClause<'tcx>, Span>,
)

Given a requirement T: 'a or 'b: 'a, deduce the outlives_component and add it to required_clauses