Merge branch 'fix-deferred-delete' into 'master'
Fix deferred vertex deletion, add unit tests. GeometryKernel::collect_garbage used to first perform the TopologyKernel garbage collection, usually shrinking its vertex_deleted_ member, then accessed it using is_deleted() with the old vertex indices. This caused out-of-bounds memory access (made visible by cmake -DSTL_VECTOR_CHECKS=ON) and non-fast deletion also resulted in wrong results, the remaining vertices had wrong coordinates. See merge request !4