Parent-Task:

• SR-13659 Retroactive derivative registration

relates to:

• TF-1025 using default @differentiable function arguments from multiple files causes duplicate definition of diff witness
• TF-690 [AD] Linker error regarding AD associated functions of default argument closures

Issue Description:

Some bugs are probably caused by incorrect linkage, or bad interactions between serialization and linkage (TF-1025, TF-690).

The error mentioned here #28532 (comment) is probably also caused by this.

We should carefully think through linkage and serialization for ad symbols and come up with a simple, robust solution.

Note: Check if there is existing SIL infra for determining linkage of generated things.