Add more comments, fix format issues

include/grpc++/ext/proto_server_reflection_plugin.h

src/cpp/ext/proto_server_reflection.cc

src/cpp/ext/proto_server_reflection.h

src/cpp/ext/proto_server_reflection_plugin.cc

test/cpp/util/proto_reflection_descriptor_database.h

tools/distrib/check_include_guards.py

...ckerfile/grpc_clang_format/clang_format_all_the_things.sh

tools/run_tests/sanity/check_sources_and_headers.py