MDEV-26929: Make the main testsuite runnable with optimizer trace enabled

Part#2: check that compile-time default @@optimizer_trace is correct.

mysql-test/main/opt_trace_default.result

+# Verify that compile-time default for optimizer trace is OFF (enabled=off).
+select
+global_value_origin,
+default_value
+from
+INFORMATION_SCHEMA.SYSTEM_VARIABLES where variable_name='optimizer_trace';
+global_value_origin	default_value
+COMPILE-TIME	enabled=off

mysql-test/main/opt_trace_default.test

+
+if (`SELECT 'COMPILE-TIME'<>GLOBAL_VALUE_ORIGIN from INFORMATION_SCHEMA.SYSTEM_VARIABLES where variable_name='optimizer_trace'`) {
+--Skip Needs optimizer_trace default to be the compile-time default
+}
+
+--echo # Verify that compile-time default for optimizer trace is OFF (enabled=off).
+select
+  global_value_origin,
+  default_value
+from
+  INFORMATION_SCHEMA.SYSTEM_VARIABLES where variable_name='optimizer_trace';