process: cleanup and document the bootstrap process in bootstrap/node.js

lib: move per_context.js under lib/internal/bootstrap

process: document the bootstrap process in node.js

lib: save a copy of Symbol in primordials

process: use primordials in bootstrap/node.js

process: refactor lib/internal/bootstrap/node.js

• Use deprecate from internal/util instead of from util
• Split setupGlobalVariables() into setupGlobalProxy() and setupBuffer(), and move out manipulation of the process object.

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