Support "-" in database table names

Problem/Motivation

Documentation on SelectInterface::leftJoin():

   * @param $table
   *   The table against which to join. May be a string or another SelectQuery
   *   object. If a query object is passed, it will be used as a subselect.
   *   Unless the table name starts with the database / schema name and a dot
   *   it will be prefixed.

Which means you can pass the fully qualified table name to this method, inlcuding the database name. If your database name is "drupal-8" (valid in MySQL) you should be able to pass in "drupal-8.node" if you want to join to the node table for example. The problem is that some escape*() method on Drupal\Core\Database\Connection strips the "-" character from that string. Your query will have a join to "drupal8.node", which of course refers to a completely different database and MySQL will throw an access denied error or an exception that the database does not exist.

Proposed resolution

Never use "-" in your MySQL database names, although it is allowed!

Or we could fix the MySQL driver to properly support "-".

Remaining tasks

?

User interface changes

none.

API changes

none.

Data model changes

none.