Final interface of SchemaShape

[Zruty0]

1. Move to Microsoft.ML.Data
2. internal-best-friend all methods that are not accessing columns.
3. Make SchemaShape be a IReadOnlyList<SchemaShape.Column>
4. Add an accessor by name, and GetColumnOrNull, like Schema has.
5. Make SchemaShape.Column a struct.
6. Remove SchemaException.

[sfilipi]

@Zruty0

3. Make SchemaShape be a IReadOnlyList<SchemaShape.Column>

Do you mean the Column[] Columns inside the SchemaShape should convert toIReadOnlyList<SchemaShape.Column> ?

[Zruty0]

No, I mean the class itself should be IReadOnlyList<SchemaShape.Column>. This is to be more parallel to Schema class, which it resembles.

[wschin]

We already have

        /// <summary>
        /// Returns if there is a column with a specified <paramref name="name"/> and if so stores it in <paramref name="column"/>.
        /// </summary>
        public bool TryFindColumn(string name, out Column column)
        {
            Contracts.CheckValue(name, nameof(name));
            column = Columns.FirstOrDefault(x => x.Name == name);
            return column.IsValid;
        }

so we don't need to do (4). Task (1) had been done as well.