vbo/dlist: reallocate the vertex buffer on vertex upgrade
upgrade_vertex
copies save->copied.nr
vertices to the vertex buffer,
so we need to make sure it has enough space to accomodate them.
This commit also drops the usage of COPY_CLEAN_4V_TYPE_AS_UNION
in
this function because it always writes 4-components for all attributes,
but our buffer might be smaller. Instead, only write the needed
components.
Closes: #5353 (closed) Fixes: cc57156d ("vbo/dlist: rework vertex_store management")