Implement the new JSX transform function

[bqqbarbhg]

Implement the new JSX transform function in kaiku. This allows kaiku to be used without having to import or specify the JSX factory function h().

The jsx() function differs from the legacy h() JSX factory in signature and thus needs specific support. I opted to implement jsx() directly instead of wrapping h() as that would lead into double copying of props which would hurt performance. The size overhead of this approach is 80 bytes in the final gzipped bundle:

baseline raw   6,98 KB (7 150 bytes)
jsx() raw      7,21 KB (7 387 bytes)
baseline gzip  2,91 KB (2 983 bytes)
jsx() gzip     2,99 KB (3 063 bytes)

The cost in size by keeping both h() and jsx() allows users to use either JSX transform without any additional configuration, which in my user-focused opinion seems like a fair tradeoff.

For further development adding key to element descriptors directly and allowing children to be a single element value would allow us to use props directly without copying in the descriptor instances which would reduce a ton of unnecessary allocations and object copies during component rendering.