Slim down the library size

According to https://bundlephobia.com/package/typechain@8.0.0, this lib is 558kb big (minified), which is not acceptable for consumers who want to offer a fast web experience. Additionally, not every user has an infinite amount of bandwidth available to download excessive data.

There are two dependencies that seem to cause most of the bundle size bloat:
- `prettier` is bundled as prod dep, is there a chance to make it optional or put it into devDeps? I found this related issue: https://github.com/dethcrypto/TypeChain/issues/570
- `lodash` is easy to use but makes up 20% of the bundle size of this lib, most of the methods can be easily replaced with native JS, e.g. https://github.com/you-dont-need/You-Dont-Need-Lodash-Underscore#_flatten