[gem] Use decorators instead constructor params

[mantou132]

Easy to extends

@shadow()
@delegatesFocus()
@serializable()
@slotAssignment()
@focusable()
@async()
@role('button')
class MyElement extends GemElement {}

@shadow({ delegatesFocus: false }) // serializable/slotAssignment
@focusable()
@async()
@role('button')
class MyElement extends GemElement {}

@shadow({ delegatesFocus: false }) // serializable/slotAssignment
@focusable()
@async()
@aria({ role: 'button' })
class MyElement extends GemElement {}

@shadow(true) // serializable/slotAssignment
@focusable()
@async()
@aria('button') // label/ariaModal
class MyElement extends GemElement {}

add GemElement.config

[mantou132]

@async => @noblocking