wt-status: add VFS hydration percentage to normal git status output

Add VFS checkout hydration percentage information to the default `git
status` output.  When VFS is enable, users will now see a "You are in
a partially-hydrated checkout with <percentage> of tracked files
present." message.

Upstream `git status` normally prints a "You are in a sparse checkout
with <percentage> of tracked files present."  This message was hidden
in `microsoft/git` when `core_virtualfilesystem` is set (because GVFS
users are always (and secretly) in a sparse checkout) and it was
thought that it would annoy users.

However, we now believe that it may be helpful for users to always see
the percentage and know when they are over-hyrdated, since
over-hyrdation can occur by accident and may greatly impact their Git
performance.  Knowing this value may help with GVFS support.

Helped-by: Johannes Schindelin <johannes.schindelin@gmx.de>
Signed-off-by: Jeff Hostetler <jeffhostetler@github.com>

t/t1093-virtualfilesystem.sh

@@ -69,6 +69,8 @@ test_expect_success 'verify status is clean' '
 	git status > actual &&
 	cat > expected <<-\EOF &&
 		On branch main
+		You are in a partially-hydrated checkout with 75% of tracked files present.
+
 		nothing to commit, working tree clean
 	EOF
 	test_cmp expected actual

wt-status.c

@@ -1604,10 +1604,15 @@ static void show_sparse_checkout_in_use(struct wt_status *s,
 {
 	if (s->state.sparse_checkout_percentage == SPARSE_CHECKOUT_DISABLED)
 		return;
-	if (core_virtualfilesystem)
-		return;
-
-	if (s->state.sparse_checkout_percentage == SPARSE_CHECKOUT_SPARSE_INDEX)
+	if (core_virtualfilesystem) {
+		if (s->state.sparse_checkout_percentage == SPARSE_CHECKOUT_SPARSE_INDEX)
+			status_printf_ln(s, color,
+					 _("You are in a partially-hydrated checkout with a sparse index."));
+		else
+			status_printf_ln(s, color,
+					 _("You are in a partially-hydrated checkout with %d%% of tracked files present."),
+					 s->state.sparse_checkout_percentage);
+	} else if (s->state.sparse_checkout_percentage == SPARSE_CHECKOUT_SPARSE_INDEX)
 		status_printf_ln(s, color, _("You are in a sparse checkout."));
 	else
 		status_printf_ln(s, color,