C++20 compat: use invoke_result_t instead of result_of am: 355831b13d

Original change: https://android-review.googlesource.com/c/platform/external/grpc-grpc/+/2980335

Change-Id: I3a2ad283a0d92dbcf51de09b14761763bd333f39
Signed-off-by: Automerger Merge Worker <android-build-automerger-merge-worker@system.gserviceaccount.com>