Introduce vendor_apex_metadata_file

A new label for ./apex_manifest.pb and ./ entries in vendor apexes. This
is read-allowed by a few system components which need to read "apex" in
general. For example, linkerconfig needs to read apex_manifest.pb from
all apexes including vendor apexes.

Previously, these entries were labelled as system_file even for vendor
apexes.

Bug: 285075529
Test: m && launch_cvd
Test: atest VendorApexHostTestsCases
Change-Id: Icc234bf604e3cafe6da81d21db744abfaa524dcf
diff --git a/private/shell.te b/private/shell.te
index 85d09f9..181963c 100644
--- a/private/shell.te
+++ b/private/shell.te
@@ -136,6 +136,7 @@
 allow shell apex_info_file:file r_file_perms;
 allow shell vendor_apex_file:file r_file_perms;
 allow shell vendor_apex_file:dir r_dir_perms;
+allow shell vendor_apex_metadata_file:dir r_dir_perms;
 
 # Allow shell to read updated APEXes under /data/apex
 allow shell apex_data_file:dir search;