Revamp `cg_llvm` debuginfo handling to use records

[workingjubilee]

Currently, we use debuginfo driven by intrinsics. We will need to use records instead, see the migration doc released with LLVM 19: https://llvm.org/docs/RemoveDIsDebugInfo.html

Some notes:

• Most of the functions we want should be exported in the LLVM-C API already, see Revamp cg_llvm debuginfo handling to use the LLVM-C API #134001 and https://github.com/llvm/llvm-project/blob/main/llvm/include/llvm-c/DebugInfo.h
• We will need to make this logic conditional on what version of LLVM is in use until we raise our LLVM minimum to 19.
• They say "This should happen transparently when using the DIBuilder to construct debug variable information, but will require changes for any code that interacts with debug intrinsics directly." so we may have to do... nothing at all! This issue was filed before determining what specific changes we have to make.

[nikic]

I don't think we need to change anything for this.

[workingjubilee]

This does indeed seem to have been the case! We have a few mentions of these debug intrinsics in our codebase but we don't actually call them directly, unlike other intrinsics. We call the builder "properly".