feat(sfc): support using extends interface with defineProps()

[edison1105]

close #4498

[oooplz]

~~Why do the feat still no be merged to master branch.~~

My apologies for the ask. I am using vue-next to develop a lib. And i have one component should be creating some child components. So i thought the extends keyword was helpful for me.

But @yyx990803 has said that the workaround is to prefer writing props types in the same file instead of importing it.

Maybe the feat should be discussed.

[sambitevidev]

Is it going to be merged ?

[AisonSu]

Is it going to be merged ?

[brocjo]

Merge progress? Anyone have any clever workarounds? This would go a long way in helping abstract out some complicated bits of our component library...

[wvffle]

Over a year has passed since this PR got created :/ Merging it would help to really simplify our project :)