Support the NPM node_modules dir

This commit adds support for the node_modules directory. This support includes
caching of the directory between invocations of the buildpack, rebuilding the
modules if the version of node has changed and pruning modules that are no
longer required. Previousley there was no support beyond building node_modules
from scratch on every invocation of the buildpack.

[#71846468]
[#71846626]
[#71846678]