Conservative stack scanning for GC safe ccalls

[qinsoon]

The issue was raised in JuliaLang/julia#57297 that some threads are not stopped for GC thus the introduced method is not called for those threads, and we do not scan the registers for those threads.

We need to find out the semantics of the GC safe ccalls, and deal with the potential object references they may access. Diogo mentioned that there is a mechanism to stop threads with a signal, and do scanning there before a GC. Steve mentioned that we may do transitive pinning for what the threads may access.

Related links:

• jl_gc_safe_enter
• Allow for :foreigncall to transition to GC safe automatically JuliaLang/julia#49933
• ccall gc_safe
• GC-safe ccalls JuliaLang/julia#51574
• https://github.com/JuliaLang/julia/blob/f7b986d138b062795048e5992aea31aad5c8a306/src/julia_threads.h#L139-L145