[SPIR-V] Implement correct zeroinitializer for extension types in SPIR-V Backend (#93607)

This PR implements correct zeroinitializer for extension types in SPIR-V
Backend.

Previous version has just created 0 of 32/64 integer type (depending on
target machine word size), that caused re-use and type re-write of the
corresponding integer constant 0 with a potential crash on wrong usage
of the constant (i.e., 0 of integer type expected but extension type
found). E.g., the following code would crash without the PR:

```
  %r1 = icmp ne i64 %_arg_i, 0
  %e1 = tail call spir_func target("spirv.Event") @__spirv_GroupAsyncCopy(i32 2, ptr addrspace(3) %_arg_local, ptr addrspace(1) %_arg_ptr, i64 1, i64 1, target("spirv.Event") zeroinitializer)
```

because 0 in icmp would eventually be of `Event` type.
3 files changed
tree: 62f0a8eaf6f4b91e0a2d20ed5d54c6d46802abec
  1. .ci/
  2. .github/
  3. bolt/
  4. clang/
  5. clang-tools-extra/
  6. cmake/
  7. compiler-rt/
  8. cross-project-tests/
  9. flang/
  10. libc/
  11. libclc/
  12. libcxx/
  13. libcxxabi/
  14. libunwind/
  15. lld/
  16. lldb/
  17. llvm/
  18. llvm-libgcc/
  19. mlir/
  20. offload/
  21. openmp/
  22. polly/
  23. pstl/
  24. runtimes/
  25. third-party/
  26. utils/
  27. .clang-format
  28. .clang-tidy
  29. .git-blame-ignore-revs
  30. .gitattributes
  31. .gitignore
  32. .mailmap
  33. CODE_OF_CONDUCT.md
  34. CONTRIBUTING.md
  35. LICENSE.TXT
  36. pyproject.toml
  37. README.md
  38. SECURITY.md
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