Unifying variable names representing a table name in the Schema system

While working on #4505, I noticed that in the Schema system, variables representing a table name did not always have the same name, which confused me at first.
Sometimes it was `$table`, sometimes it was `$name`. This PR aims to unify the name used accross the Schema system.

I went for `$tableName` as `$table` is already used in some methods but needs to be a \Schema\Table instance.