Added methods to support custom data types.

[coolamit]

This is a followup to #91.

This PR adds support for custom data types - create, alter, and drop.

Schema facade gets these additions:

Schema::changeType(string $name, ?string $alteration = null): void
Schema::changeTypeName(string $name, string $newName): void
Schema::changeTypeToAddEnumValue(string $name, string $newValue): void
Schema::changeEnumTypeValueName(string $name, string $existingValue, string $newValue): void
Schema::createType(string $name, string $type): void
Schema::dropType(string ...$name): void
Schema::dropTypeIfExists(string ...$name): void

Blueprint class gets this addition

public function type(string $column, string $type): ColumnDefinition

The type() method above is just syntactic sugar, a wrapper around the domain() method, to allow for expressive code when assigning a custom data type to a column.

[coolamit]

@tpetry Please take a look

[tpetry]

Thanks for your contribution @coolamit but I won't merge this PR.

The PostgreSQL CREATE TYPE command is creating more trouble than it benefits an application from my experience:

• ENUM is not really used in PG because it has one serious drawback: You can't remove any value from the enum anymore like in MySQL. That's the reason why ENUMs are not used with PG. Even Laravel doesn't use them with the ->enum() type and prefers the better approach of using a string type with a CHECK constraint. And you can also create types with check constraint: domain types!
• Composite types are also a great idea in theory. But serializing and deserializing is quite complicated and can easily lead to SQL injections when not all cases are handled correctly and placeholders are not used.