Add property defaults assembler

[veewee]

This PR introduces a new PropertyDefaultsAssembler:

The encoding library is less forgiving about missing information in requests than PHP's soap encoder.
This assembler allows you to e.g. set default property values for request objects, so that you only have to fill in the data you care about.

Example configuration:

$config
    ->addRule(
        new Rules\IsRequestRule(
            $meta,
            new Rules\MultiRule([
                new Rules\AssembleRule(new Assembler\ImmutableSetterAssembler()),
                new Rules\AssembleRule(new Assembler\RequestAssembler()),
                new Rules\AssembleRule(new Assembler\PropertyDefaultsAssembler())
            ])
        )
    )

It works together with the PropertyAssembler and will enhance the default value generation for :

• mixed => null
• string => ''
• int => 0
• float => 0.0
• bool => false
• array => []

Example:

    /**
     * @var int
     */
    private int $quantity = 0;