[HAL] Add executable global lookup buffers (#24336)

Introduces iree_hal_executable_lookup_global_by_name as the public HAL
API for resolving executable-owned globals. The API returns a normal
iree_hal_buffer_t so callers can use existing queue copies, mapping
checks, and command-buffer bindings instead of reaching around HAL with
raw device pointers.

AMDGPU resolves HSA variable symbols for the selected queue-affinity
device and wraps the variable address as non-owning executable-backed
storage. HIP and CUDA use their module global lookup APIs and wrap
external device pointers with the same lifetime rule. Returned buffers
retain the executable until the buffer is released.

All executable vtables now implement the hook explicitly. Backends
without global support fail with UNIMPLEMENTED, and replay recording
fails loudly rather than returning an unrecorded buffer object.

(cherry pick from #24049 with CUDA + AMDGPU support as well as HIP)

Co-authored-by: Andrew Woloszyn <andrew.woloszyn@gmail.com>