Merge branch 'ds/sparse-index-ignored-files'

In cone mode, the sparse-index code path learned to remove ignored files (like build artifacts) outside the sparse cone, allowing the entire directory outside the sparse cone to be removed, which is especially useful when the sparse patterns change. * ds/sparse-index-ignored-files: sparse-checkout: clear tracked sparse dirs sparse-index: add SPARSE_INDEX_MEMORY_ONLY flag attr: be careful about sparse directories sparse-checkout: create helper methods sparse-index: use WRITE_TREE_MISSING_OK sparse-index: silently return when cache tree fails unpack-trees: fix nested sparse-dir search sparse-index: silently return when not using cone-mode patterns t7519: rewrite sparse index test