Add support for DropDatabase

[scorixear]

Checklist

• I have read the Contributing Guide
• I have checked to ensure this does not introduce an unintended breaking changes
• I have considered appropriate testing for my change

Description

Adds three additional extension methods for SupportedDatabasesForDropDatabase allowing MySql to be used
in the same manner as the DbUp.SqlServer package.

DbUp.DropDatabase.For.MySqlDatabase(connectionstring);

Method signatures and implementation are mainly taken from DbUp.SqlServer and the already existent SupportedDatabasesForEnsureDatabase extension methods.

DbUp.SqlServer introduces an additional alter statement before dropping

ALTER DATABASE [{databaseName}] SET SINGLE_USER WITH ROLLBACK IMMEDIATE;

There is no equivalent in MySql for this.
The possibility to read lock all databases with

FLUSH TABLES WITH READ LOCK;

was considered but not implemented as it affects all databases. The drop command will fail fast, if any connection is still present.

[droyad]

Very nice, thank you. Going into v5.

[scorixear]

@droyad Not sure why the test is failing, I have reordered the methods in the ApprovalFiles, maybe that fixes something