Rename `connection` to `dataSource` in `EntityManager`, `Repository`, `QueryBuilder`, `QueryRunner` etc. Create deprecated alias for backwards-compatibility.

Rename `connection` to `dataSource` in `EntityManager`, `Repository`, `QueryBuilder`, `QueryRunner`, `EntityMetadata`, `*Event` etc.

Create deprecated getter for backwards-compatibility.

Step 1: `Driver`, `QueryRunner`
Step 2: `EntityManager`, `QueryBuilder`
Step 3: `*Event`
Step 4: `*Metadata` / other internals