Full debug: emit source-facing device function names and linkage names #1122

Description

cuda-oxide currently writes the physical/exported device symbol into
DISubprogram.name and emits no linkageName. Source-qualified function
breakpoints therefore remain pending even though a breakpoint on the physical
symbol resolves.

This is a child of #226.

Minimal reproducer

With full device debug information, set cuda-gdb breakpoints on a qualified
non-generic helper and on a fully specialized generic device method. The
cuda-devtools T02 assessment demonstrates the failing generic-method case; a
non-generic control such as debuginfo::deep_outer rules out generic syntax as
the root compiler defect.

Expected behavior

DWARF carries a source-facing canonical function identity separately from the
unchanged physical symbol, so cuda-gdb can index qualified source names without
changing ABI/export behavior.

Actual behavior

On baseline 6c5458fe, debuginfo::deep_outer remains pending while the
physical debuginfo__deep_outer symbol hits. Generic methods are listed only
under raw mangled names. DISubprogram has the physical spelling as name and
no linkageName.

Acceptance criteria

• Carry source-facing/canonical debug identity separately from the physical
  linkage/export name.
• Definitions emit human name plus exact physical linkageName without
  changing symbols or ABI.
• Inline scopes use a proven canonical source name and do not invent a linkage
  name.
• cuda-gdb resolves a qualified non-generic helper and an exact fully
  specialized generic/device method.
• Tests cover kernels with export overrides, two generic monomorphizations,
  inline scopes, full/line-table modes, LLVM verification, and live cuda-gdb.

Out of scope / follow-up

The generic-eliding shorthand cuda_device::DisjointSlice::get_mut is not a
canonical unique monomorphization name. Supporting that alias requires proper
namespace/type DIEs or an agreed debugger alias policy. The assessment should
use the canonical specialized spelling until that work is defined.

Environment

• Baseline: 6c5458fe991bbde32c5bee74d87822aef1b5a691
• CUDA/cuda-gdb: 13.3
• GPU: RTX 5090 (sm_120)