[FEATURE REQUEST] Support typescript decorators

In ts config

...
"experimentalDecorators": true,
...

in ts code

class BigButton extends Button {
...
    @someDecorator()
    fun1() {}
...
}

What to expect:

We hope the decorator will be compiled in target js file

Current:

In js file, the decorator only imported but not used

More info:

I try to write a babel plugin to handle the decorator, but when the babel visit the ClassMethod node, what I found:

1. node.decorators is null
2. the function name should be fun1, but what I get is _fun1

But when I remove the transform-ui5 preset, all information is correct.

Start by reproducing the TypeScript example with experimentalDecorators enabled and the transform-ui5 preset, then inspect the Babel ClassMethod visitor. Compare the AST with and without transform-ui5; done means the decorator is emitted and used in the target JavaScript rather than only imported, while the method remains correctly identified.