src: move C++ binding/addon related code into node_binding{.h, .cc}

This patch:

- Moves the C++ binding/addon related code out of
  node_internals.h/node.cc and into dedicated files
  node_binding.h/node_binding.cc, and only puts the code resued
  by other files into the header.
- Introduce a node::binding namespace so that code exposed to
  other files can be easily recognized.

PR-URL: nodejs#24701
Reviewed-By: Ben Noordhuis <info@bnoordhuis.nl>
Reviewed-By: Richard Lau <riclau@uk.ibm.com>

node.gyp

@@ -343,6 +343,7 @@
         'src/module_wrap.cc',
         'src/node.cc',
         'src/node_api.cc',
+        'src/node_binding.cc',
         'src/node_buffer.cc',
         'src/node_config.cc',
         'src/node_constants.cc',
@@ -414,6 +415,7 @@
         'src/node.h',
         'src/node_api.h',
         'src/node_api_types.h',
+        'src/node_binding.h',
         'src/node_buffer.h',
         'src/node_constants.h',
         'src/node_context_data.h',