Reduce reflect-metadata dependency size

[dulowski-marek]

Problem
Currently https://github.com/rbuckton/reflect-metadata is used, which provides its own polyfills for objects like WeakMap. There's an issue aiming to solve it, but there's no response (rbuckton/reflect-metadata#73).

Due to how reflection works under the hood, the package makes its way into consumer bundle, which adds large size overhead unnecessarily.

Solution
There's an alternative implementation of metadata proposal which is sufficient - https://github.com/abraham/reflection , which should be used.