Build: Generate the slim build on `grunt` & run `compare_size` on it

Build: Generate the slim build on `grunt` & run `compare_size` on it

Summary of the changes:
* expand `node_smoke_tests` to test the full & slim builds
* run `compare_size` on all built minified files; don't run it anymore on
  unminified files where they don't provide lots of value

The main goal of this change is to make it easier to compare sizes of both the
full & slim builds between the `3.x-stable` & `main` branches.

Closes gh-5291
Ref gh-5255

(partially cherry-picked from commit 8be4c0e4f89d6c8f780e5937a0534921d8c7815e)