Support GN build without using depot_tools

[zcbenz]

The GN build is documented at #51676, which however requires using depot_tools from Chromium for building, and the code of Node must be checked out in a specific directory structure.

To simplify the GN build for developers who don't work with Chromium, there has been an effort to make GN work without depot_tools:

• The https://github.com/yue/build-gn is a fork of GN that bundles the build configurations of Chromium with it.
• The https://github.com/photoionization/node_with_gn makes uses of the forked GN to build Node without depot_tools.

There are a few problems left for solving:

• Maintaining the forked GN is a burden.
• Even without the requirement of depot_tools, the GN build of V8 requires the following dependencies to exist:
  • abseil-cpp
  • icu
  • jinja2
  • markupsafe
  • zlib
• The default configurations of V8 does not work with Node, and we must explicitly pass a list of GN args when generating the build files.

[targos]

the GN build of V8 requires the following dependencies to exist

Is it an issue even though we include the source of these dependencies in our tree?

[zcbenz]

The GN files of V8 hardcodes paths to some dependencies to //third_party/xxx, I need to add args to allow changing them to //node/deps/xxx to fix them.

[targos]

OK for icu. The other ones are in the third_party directory.