src: remove calls to deprecated v8 functions (NewFromUtf8)

Remove all calls to deprecated v8 functions (here: String::NewFromUtf8) inside the code (src directory only).

Checklist

• make -j4 test (UNIX), or vcbuild test (Windows) passes
• tests and/or benchmarks are included
• documentation is changed or added
• commit message follows commit guidelines

Files

• src/async_wrap.cc
• src/cares_wrap.cc
• src/env-inl.h
• src/exceptions.cc
• src/heap_utils.cc
• src/module_wrap.cc
• src/node.cc
• src/node.h
• src/node_api.cc
• src/node_config.cc
• src/node_crypto.cc
• src/node_file.cc
• src/node_i18n.cc
• src/node_internals.h
• src/node_os.cc
• src/node_perf.cc
• src/node_process.cc
• src/node_trace_events.cc
• src/node_url.cc
• src/node_util.cc
• src/node_v8.cc
• src/spawn_sync.cc
• src/string_bytes.cc
• src/string_decoder.cc