Offer a modern build without ES5 transpilation

## Summary

Requesting a build of the Amplitude Browser SDK that does not transpile syntax supported by most browsers for a few years.

## Motivations

My employer is using Amplitude, and we've noticed that the Amplitude TypeScript Browser SDK is compiling post-ES5 syntax (classes, async/await, rest args, etc) to ES5-compatible syntax. This works, but adds additional network I/O for our users (we do not support pre ES2015 JS engines).

We'd like to request that the npm package begin publishing non-transpiled standard JavaScript as an additional option, in addition to the CJS and ESM builds.

## Screenshots

### Example of build output set to target: es5

### Example of build output set to target: es2020