Schema factory syntax

[LucDeCaf]

Enables better syntax for building out the PowerSync schema. Related discussion can be found here.

The reasoning for using a new factory class instead of modifying the base Table class is that the syntax shown in this PR requires the properties being set to be mutable, but the Table class is not designed to be modified after construction. Therefore, we use a mutable factory class which can produce immutable Table classes. This PR also restricts access to Table's accessers in order to reflect this change.

Breaking changes:

• Table name must now be passed in the Table constructor instead of in the Schema constructor
• Some fields in PowerSync.Common.DB.Schema.Table have been made private/readonly
• Renamed ColumnType enum from SCREAMING_SNAKE_CASE to PascalCase