Typed src prop for next/image for images stored in the public directory

[PlagueFPS]

Goals

1. Prevent invalid references to non-existent images
2. Improve confidence and developer velocity when referencing public assets
3. Provide build time errors for invalid references instead of runtime

Non-Goals

Background

This feature would be extremely useful for anyone referencing static public assets in their next/image components instead of importing the images directly, as such, with dynamic image referencing from data, or in MDX content, where directly importing images into the MDX file can bloat the serverless function size and exceed the maximum 300mb limit.

The current alternative is to write your own local script that generates the types.

Proposal

This feature should be implemented by scanning the directories and files within the public directory and forming a type union of relative image paths to use on the src property of the next/image component.

This type should also be exported so that users can easily extend the next/image functionality with their own wrapper image components, which is quite common.

I also believe this should run on next typegen and during the dev server start, similar to the current Page and Route Helpers @bgub merged in v15.5, and watch the public directory for any changes while the dev server is running to re-generate types, just like the route types.