Merge pull request #414: Make sparse index the default

This branch is exactly #410, but with one more commit: enabling the sparse index by default in d59110a.

Having this in the `vfs-2.33.0` branch helps build confidence that the sparse index is doing what it should be doing by running in the Scalar functional tests and in our test branches.

If we want to cut a new `microsoft/git` release without enabling the sparse index, we can simply revert this commit.

repo-settings.c

@@ -71,7 +71,7 @@ void prepare_repo_settings(struct repository *r)
 	repo_cfg_bool(r, "pack.usesparse", &r->settings.pack_use_sparse, 1);
 	repo_cfg_bool(r, "pack.usepathwalk", &r->settings.pack_use_path_walk, 0);
 	repo_cfg_bool(r, "core.multipackindex", &r->settings.core_multi_pack_index, 1);
-	repo_cfg_bool(r, "index.sparse", &r->settings.sparse_index, 0);
+	repo_cfg_bool(r, "index.sparse", &r->settings.sparse_index, 1);
 	repo_cfg_bool(r, "index.skiphash", &r->settings.index_skip_hash, r->settings.index_skip_hash);
 	repo_cfg_bool(r, "pack.readreverseindex", &r->settings.pack_read_reverse_index, 1);
 	repo_cfg_bool(r, "pack.usebitmapboundarytraversal",

t/perf/p2000-sparse-operations.sh

@@ -56,7 +56,7 @@ test_expect_success 'setup repo and indexes' '
 	git -c core.sparseCheckoutCone=true clone --branch=wide --sparse . full-v3 &&
 	(
 		cd full-v3 &&
-		git sparse-checkout init --cone &&
+		git sparse-checkout init --cone --no-sparse-index &&
 		git sparse-checkout set $SPARSE_CONE &&
 		git config index.version 3 &&
 		git update-index --index-version=3 &&
@@ -65,7 +65,7 @@ test_expect_success 'setup repo and indexes' '
 	git -c core.sparseCheckoutCone=true clone --branch=wide --sparse . full-v4 &&
 	(
 		cd full-v4 &&
-		git sparse-checkout init --cone &&
+		git sparse-checkout init --cone --no-sparse-index &&
 		git sparse-checkout set $SPARSE_CONE &&
 		git config index.version 4 &&
 		git update-index --index-version=4 &&

t/t1092-sparse-checkout-compatibility.sh

@@ -155,6 +155,7 @@ init_repos () {
 	git -C sparse-index reset --hard &&
 
 	# initialize sparse-checkout definitions
+	git -C sparse-checkout config index.sparse false &&
 	git -C sparse-checkout sparse-checkout init --cone &&
 	git -C sparse-checkout sparse-checkout set deep &&
 	git -C sparse-index sparse-checkout init --cone --sparse-index &&

t/t7817-grep-sparse-checkout.sh

@@ -49,7 +49,7 @@ test_expect_success 'setup' '
 		echo "text" >B/b &&
 		git add A B &&
 		git commit -m sub &&
-		git sparse-checkout init --cone &&
+		git sparse-checkout init --cone --no-sparse-index &&
 		git sparse-checkout set B
 	) &&