MDEV-31608 - Connector/NET fails to connect since 10.10

Connector/NET does not expect collation IDs returned by "show collations"
to be NULL, runs into an exception.

The fix is to determine connector/net using its connection attributes,
then make sure "show collations" does not output NULL IDs.

The patch introduces new old_mode NO_NULL_COLLATION_IDs, that is
automatically set, once MySQL Connector/NET connection is determined.

A test was added, that uses MySql.Data from powershell - only works
if MySql.Data is installed into GAC (i.e with C/NET MSI package)

mysql-test/main/mysql_connector_net.test

@@ -0,0 +1,11 @@
+--source include/windows.inc
+let $sys_errno=0;
+
+# Error 100 is returned by the powershell script
+# if MySql.Data is not installed
+--error 0,100
+--exec powershell -NoLogo -NoProfile -File main\mysql_connector_net.ps1
+if ($sys_errno != 0)
+{
+  --skip Connector/NET is not installed
+}