Increase number of max table_open_cache instances

This is a backport of MDEV-11429 from 10.1

mysql-test/suite/sys_vars/r/table_open_cache_basic.result

@@ -27,7 +27,7 @@ Warnings:
 Warning	1292	Truncated incorrect table_open_cache value: '1073741824'
 SELECT @@global.table_open_cache ;
 @@global.table_open_cache
-524288
+1048576
 SET @@global.table_open_cache  = 18000;
 SELECT @@global.table_open_cache ;
 @@global.table_open_cache
@@ -48,7 +48,7 @@ Warnings:
 Warning	1292	Truncated incorrect table_open_cache value: '100000000000'
 SELECT @@global.table_open_cache ;
 @@global.table_open_cache
-524288
+1048576
 SET @@global.table_open_cache = -1024;
 Warnings:
 Warning	1292	Truncated incorrect table_open_cache value: '-1024'

sql/sys_vars.cc

@@ -3059,7 +3059,7 @@ static bool fix_table_open_cache(sys_var *, THD *, enum_var_type)
 static Sys_var_ulong Sys_table_cache_size(
        "table_open_cache", "The number of cached open tables",
        GLOBAL_VAR(tc_size), CMD_LINE(REQUIRED_ARG),
-       VALID_RANGE(1, 512*1024), DEFAULT(TABLE_OPEN_CACHE_DEFAULT),
+       VALID_RANGE(1, 1024*1024), DEFAULT(TABLE_OPEN_CACHE_DEFAULT),
        BLOCK_SIZE(1), NO_MUTEX_GUARD, NOT_IN_BINLOG, ON_CHECK(0),
        ON_UPDATE(fix_table_open_cache));