MDEV-32901: innodb.mdev-14846 fails in 11.0

InnoDB could return off-by-1 estimates for the involved tables.
This would cause off-by-many difference in join output cardinality
for the top-level SELECT, and so different query plan for the subquery.

The fix: Introduce mysql-test/include/innodb_stable_estimates.{inc,opt}
which disables InnoDB's background statistics collection, and use it.

mysql-test/include/innodb_stable_estimates.inc

@@ -0,0 +1,12 @@
+#
+# Include this file in your .test file if your testcase uses InnoDB tables
+# requiring stable query plans, which likely requires that InnoDB produces
+# stable estimates for #records in tables.
+#
+# How it works:
+# Unstable InnoDB estimates are caused by InnoDB's background statistics
+# collection. When you include this file, MTR will use server options from
+# include/innodb_stable_estimates.opt, which disables background statistics
+# collection.
+# (and no, InnoDB team objects to using this configuration for all MTR tests)
+#

mysql-test/include/innodb_stable_estimates.opt

@@ -0,0 +1 @@
+--innodb_stats_auto_recalc=0

mysql-test/suite/innodb/t/mdev-14846.test

@@ -2,6 +2,8 @@
 --source include/count_sessions.inc
 --source include/have_debug_sync.inc
 
+--source include/innodb_stable_estimates.inc
+
 CREATE TABLE t1 (
  pk INT,
  f1 VARCHAR(10) NOT NULL,