[Schematic] Replace the current field definition with builder syntax

[toth-istvan-zoltan]

The current field definition syntax looks like:

class A : Schematic<A> {
    var i by int(min=12, max=24)
}

This is hard to read and problematic as we add more customisation features.

Future syntax:

class A : Schematic<A> {
    var i by int {
        constraint min 12 max 24
        constraint validator { it % 2 == 1 }
        attribute label "I"
        attribute hint "Must be odd."
        attribute doc "This is a number which must be greater than or equal to 12 and lesser than or equal to 24."
    }
}

[toth-istvan-zoltan]

This change can be done in the following ways:

• no compiler support
• builder verification in compiler plugin
• full builder translation in compiler plugin

No compiler support

Pros:

• easiest to implement and change

Cons:

• larger compiled code size (the field definition builder would take a bit more space)
• the definition is built during runtime when the class is referenced first
• the builder function compilation may result in error if it contains class field reference

Builder Verification

Pros:

• easier to implement than full translation

Cons:

• have to extend the compiler plugin
• have to interpret the builder to analyse the code

Full Builder Translation

Pros:

• most flexible in terms of result, may:
  • replace the builder fully with a field constructor call
  • serialise builder data and use an on-demand schema builder based on the serialised data
  • may be a significant code size decrease
  • may load the schema on-demand
  • may define schemas without actual classes

Cons:

• hardest to implement and change
  • compiler plugin extension
  • full code analysis and translation (might wort to have this for the future)