1.43.2 - Add possibility of nested eager load builder to throw

What's Changed

Add possibility of nested eager load builder to throw by @Frizlab in #574

This PR adds the possibility of throwing inside the block that adds nested eager loaders.
I need this because I add eager loading as needed depending on fields (user input), recursively, and I don’t know before it’s too late whether my fields are valid.

As the with functions that are modified are marked as rethrows, this should have no impact on existing code and should not require a major version bump.

This patch was released by @gwynne.

Full Changelog: 1.43.1...1.43.2