Update build

[MattiasBuelens]

• Remove down-leveling for TypeScript 3.5 or lower. It's no longer worth supporting this.
• Require Node 18 or higher. The polyfill itself should still work on older Node versions, but we're no longer testing this on the CI.
• Add polyfill.d.ts for global augmentations to the ReadableStream interface. This allows TypeScript users to use new methods such as ReadableStream.prototype[Symbol.asyncIterator](), even when TypeScript doesn't yet have a built-in type definition for them.
• Enable verbatimModuleSyntax in the TypeScript configuration. This means we have to explicitly use import type and export type.
• Manually set Function.name on class methods. This is mostly needed for the ES5 build, the modern builds already have the correct method names.
• Update a bunch of build dependencies.