PR #33470: PjRT C API: make PJRT FFI C extension header compliant

Imported from GitHub PR #33470

This PR refactors the way C structs are defined in the `pjrt_c_api_ffi_extension.h` header to use `typedef struct` instead of plain `struct`. This change improves compatibility and clarity when using these types in C code.

c/ @ezhulenev

Copybara import of the project:

--
e639338 by Hugo Mano <[email protected]>:

PjRT C API: make PJRT FFI C extension header compliant

Merging this change closes #33470

COPYBARA_INTEGRATE_REVIEW=#33470 from hugomano:hugomano/fix-pjrt-c-api-ffi-extension e639338
PiperOrigin-RevId: 827550282

Author: hugomano

xla/pjrt/c/pjrt_c_api_ffi_extension.h

@@ -32,21 +32,21 @@ extern "C" {
 // See: https://en.wikipedia.org/wiki/Foreign_function_interface
 #define PJRT_API_FFI_EXTENSION_VERSION 3
 
-struct PJRT_FFI_Type_Info {
+typedef struct PJRT_FFI_Type_Info {
   void (*deleter)(void* object);
   void (*serialize)();    // placeholder for future use
   void (*deserialize)();  // placeholder for future use
-};
+} PJRT_FFI_Type_Info;
 
-struct PJRT_FFI_Type_Register_Args {
+typedef struct PJRT_FFI_Type_Register_Args {
   size_t struct_size;
   PJRT_Extension_Base* extension_start;
 
   const char* type_name;
   size_t type_name_size;
   int64_t type_id;  // in-out
   PJRT_FFI_Type_Info* type_info;
-};
+} PJRT_FFI_Type_Register_Args;
 PJRT_DEFINE_STRUCT_TRAITS(PJRT_FFI_Type_Register_Args, type_info);
 
 // Registers external type in a static type registry. If `type_id` is set to `0`