Cranelift ARM64 / AArch64 backend: support debug info

[cfallin]

We need to propagate debug information through the new compilation pipeline in order to support several use-cases. For example, wasmtime needs this information to build a map from machine-code offsets to wasm bytecode offsets. Other use-cases may want to e.g. emit DWARF debug info in an AOT-compiled object output file.

Issue raised by @alexcrichton in the wasmtime context

cc @julian-seward1, @bnjbvr

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[bnjbvr]

This seems sensible to do, at least for debug information. This was also required for Spidermonkey before using the regular sinks (see also #1453), so there's also the possibility here to add new sinks abstractions to handle this (if it is for every single instruction, this might be high overhead, though).