MDEV-34855 Bootstrap hangs while shrinking the system tablespace

Reason:
=======
- During bootstrap, InnoDB shrinks the system tablespace while purge is
still active on system tablespace. This could lead to deadlock.

Fix:
====
Avoid System tablespace shrinking during bootstrap.
Move the shrinking logic of system tablespace after purge gets shutdown.

storage/innobase/fsp/fsp0fsp.cc

@@ -40,6 +40,9 @@ Created 11/29/1995 Heikki Tuuri
 #include "dict0mem.h"
 #include "fsp0types.h"
 #include "log.h"
+#ifndef DBUG_OFF
+# include "trx0purge.h"
+#endif
 
 /** Returns the first extent descriptor for a segment.
 We think of the extent lists of the segment catenated in the order
@@ -3576,6 +3579,8 @@ dberr_t fsp_sys_tablespace_validate()
 
 void fsp_system_tablespace_truncate()
 {
+  ut_ad(!purge_sys.enabled());
+  ut_ad(!srv_undo_sources);
   uint32_t last_used_extent= 0;
   fil_space_t *space= fil_system.sys_space;
   mtr_t mtr;

storage/innobase/handler/ha_innodb.cc

@@ -4283,12 +4283,6 @@ innobase_end(handlerton*, ha_panic_function)
 		 	}
 		}
 
-		/* Do system tablespace truncation during slow shutdown */
-		if (!srv_fast_shutdown && !high_level_read_only
-		    && srv_operation == SRV_OPERATION_NORMAL) {
-			fsp_system_tablespace_truncate();
-		}
-
 		innodb_shutdown();
 		mysql_mutex_destroy(&log_requests.mutex);
 	}

storage/innobase/srv/srv0srv.cc

@@ -1577,5 +1577,8 @@ void srv_purge_shutdown()
     }
     purge_sys.coordinator_shutdown();
     srv_shutdown_purge_tasks();
+    if (!srv_fast_shutdown && !high_level_read_only && srv_was_started &&
+        !opt_bootstrap && srv_operation == SRV_OPERATION_NORMAL)
+      fsp_system_tablespace_truncate();
   }
 }