Type hiearchy for property types and enums

[Majkl578]

This PR introduces a type hiearchy for annotation properties - types and enums.

Summary:

• introduces rather simple type hiearchy with validation and describe support;
• contains support for constant scalar types;
• describe() uses phpDoc-friendly format (plus intersections and constant values);
• validation methods return booleans instead of throwing;
• property metadata now use type objects instead of arrays for type and enum information;
• moves validation decisions out of DocParser into type objects themselves;
• moves type info formatting out of DocParser into type objects themselves.

I didn't put much effort into DocParser changes as it's eventually going to disappear.

Future scope:

• merge type and enum into one,
• rework parser for @var to properly support unions and unqualified names.

Coverage in Type namespace is 100%. 😃

[ostrolucky]

I like this overall, good job! Couple comments that need to be addressed

[Ocramius]

Overall good improvement, but some confusion between types and values (mostly a question of naming and documentation).

If we think of the definition of "type" as a "set" of possible values, then it makes sense to have IntegerType as a set of all possible int passing Type#validate(), but for ConstantType (a type that is represented by only one possible value, as far as I can see), having ConstantType#getValue() is confusing to me, and I couldn't really find usages.

The reason is that a type type doesn't "have" a value: it is logically always a set, sometimes with only ever one item, or no possible type at all, such as BottomType (impossible).

[Ocramius]

A description of the intent of this method is needed. What is the "description" you will get from this? Human-readable? Machine-friendly? An identifier? The type FQN?

[Majkl578]

for ConstantType (a type that is represented by only one possible value, as far as I can see), having ConstantType#getValue() is confusing to me, and I couldn't really find usages.

Technically getValue()is not currently needed so can as well be dropped.

[Ocramius]

Technically getValue() is not currently needed so can as well be dropped.

That's what I'm mostly sniping at

[Majkl578]

That's what I'm mostly sniping at

Dropped. 🤞

[Ocramius]

Nice work! 👍