[cfe] Verifier doesn't catch duplicate fields

[dcharkes]

writeComponentToFile fails on duplicate field, but verifyComponent does not.

Kernel print

  static final field (ffi::Pointer<ffi::Void>) → core::bool _myField$FfiNative$Ptr = ffi::_asFunctionInternal<(ffi::Pointer<ffi::Void>) → core::bool, (ffi::Pointer<ffi::Void*>*) →* ffi::Bool*>(ffi::_fromAddress<ffi::NativeFunction<(ffi::Pointer<ffi::Void*>*) →* ffi::Bool*>*>(ffi::_ffi_resolver(#C1, #C4, #C3){(core::Object, core::Object, core::int) → core::int}), true)/*isLegacy*/;
  static final field (ffi::Pointer<ffi::Void>, core::bool) → void _myField$FfiNative$Ptr = ffi::_asFunctionInternal<(ffi::Pointer<ffi::Void>, core::bool) → void, (ffi::Pointer<ffi::Void*>*, ffi::Bool*) →* ffi::Void*>(ffi::_fromAddress<ffi::NativeFunction<(ffi::Pointer<ffi::Void*>*, ffi::Bool*) →* ffi::Void*>*>(ffi::_ffi_resolver(#C1, #C4, #C5){(core::Object, core::Object, core::int) → core::int}), true)/*isLegacy*/;

Discovered in:

• Cannot use @FfiNative on both a setter and a getter. #49770

[low prio]

cc @jensjoha