This adds a "small" d.ts bundler script. This script is very basic,
using Node printing to produce its output. Generally speaking, this is
inadvisable as it completely disregards name shadowing, globals, etc.
However, in our case, we don't care about the globals, and we can opt to
restructure our codebase in order to avoid conflict, which we largely
had to do anyway when we were namespaces and everything was in scope.
This configures the existing build tasks to use esbuild by default. If
using the plain files is desired, passing `--bundle=false` will build
using plain files and still produce a runnable system.
This is only a basic build; a more efficient build is provided later
when gulp is replaced by hereby.
