Implement partial OpLine support

[khyperia]

This implements partial OpLine support. "Partial" because this only supports OpLine in two places: in types_global_values, and inside basic blocks. In reality, OpLine is allowed in types_global_values, inside basic blocks, but also between basic blocks, in the OpFunctionParameter header, between functions, after all functions, and all sorts of other wacky locations. Supporting all those wacky locations would take a fairly significant refactor (for example, adding a Vec<Instruction> in basic blocks for "OpLine/OpNoLines preceding the OpLabel instruction" - because yes, there can be multiple, if we want to faithfully represent all valid spir-v modules)

Turns out, though, this partial support is kind of all that we need in rust-gpu, we don't need to represent wacky shenanigans, so I'll leave the full refactor work up to whoever needs that functionality in the future :)

Additionally, the debug section needs to be split up into its three component subsections to not intermix OpString and OpName instructions (which, OpString is relevant to OpLine because that's how the source file is specified). The spec states:

7. These debug instructions, which must be grouped in the following order:
   a. All OpString, OpSourceExtension, OpSource, and OpSourceContinued, without forward references.
   b. All OpName and all OpMemberName.
   c. All OpModuleProcessed instructions.

I don't know why they didn't just make it three distinct "top-level" sections, because that's essentially what these subsections are, and it just causes a lot of confusion. Anyway, unfortunately, splitting up the subsections is a breaking change, so reviewers should be aware of that and consider alternatives (but I think a breaking change is the right way to go here).

[eddyb]

Tiny nit pick: looks like all the other names are pluralized, so I'd expect debug_string_sources and debug_module_processeds.