Add missing nomodule polyfills and suggest using features only up to ES2019 for browser compatibility (#15772)

These changes aim to resolve most of the concerns raised in #15756. It adds missing polyfills for legacy browsers up until ES2019:

- Number.{parseFloat,parseInt}
- ~Math.{acosh,asinh,atanh,cbrt,clz32,cosh,expm1,fround,hypot,imul,log10p,log1p,log2,sign,sinh,tanh,trunc}~ _[Removed as these are [not widely used](https://github.com/vercel/next.js/pull/15772#discussion_r463957931)]_
  - While these may seem to weigh a lot, they barely add 1 kB to the resulting bundle:
    <img width="492" alt="gzip: 32 kB vs. 30.9 kB, Brotli: 28.8 kB vs. 27.8 kB" src="https://user-images.githubusercontent.com/14854048/89100961-1376e600-d3fc-11ea-90fd-3e6632b70220.png">
- ~Object.fromEntries~ _[Removed as [it's rarely used in user code](https://github.com/vercel/next.js/pull/15772#discussion_r463984612)]_

Also, the following features are now supported with build-time transforms:

- ~`globalThis` (gets transformed into `window` in browser environments)~ _[Removed as it [could break existing applications](https://github.com/vercel/next.js/pull/15772#discussion_r463956269)]_
- `export * as ns from 'module'`

The suggested TypeScript library version has been set to ES2018, so the features below become unavailable in type-checked files (they're not evenly supported by module-compatible browsers, either):

- Object.fromEntries
- String.prototype.matchAll
- String.prototype.replaceAll
- Promise.any + AggregateError
- WeakRef

As for the `import.meta` support, [webpack v5 seems to fix that](https://github.com/webpack/webpack/pull/11075), so it should eventually become an issue of the past.

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Fixes #15756