feat: typescript project references

[samdenty]

This adds project references to the AI SDK codebase.

Improvements

• Clone codebase, install and start getting intellisense without first running build prior
• Use find all references to see everywhere something is being used
• Go to definition now goes to source files
• Rename symbol across all examples, tests etc.
• Faster full typecheck 17sec -> 1sec

Possibly breaking changes

Typescript requires the source folders to match output folders, so we would require a bunch of difference tsconfigs with circular dependencies which aren't supported.

So this PR changes the packages with multiple dist folders to instead from:

dist/index.js
anthropic/dist/index.js
...

to

dist/index.js
dist/anthropic/index.js
...

This could be a breaking change if people are depending on the filepath in the package. But if they're importing the package directly, it'll use the import map that i've updated to now use the new format (so should continue working)

[lgrammel]

Let's chat on how to best move forward w/ this. Too risky to land on main given the impact and breakages.