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.
If these are regular comments, then they won't appear in our d.ts files.
But, now we are relying on an external d.ts bundler to produce our final
merged, so they need to be present in the "input" d.ts files, meaning
they have to be JSDoc comments.
These comments only work today because all of our builds load their TS
files from scratch, so they see the actual source files and their
non-JSDoc comments.
The comments also need to be attached to a declaration, not floating,
otherwise they won't be used by api-extractor, so move them if needed.
This step converts as many explicit accesses as possible in favor of direct imports from the modules in which things were declared. This restores the code (as much as possible) back to how it looked originally before the explicitify step, e.g. instead of "ts.Node" and "ts.Symbol", we have just "Node" and "Symbol".
This step converts each file into an exported module by hoisting the namespace bodies into the global scope and transferring internal markers down onto declarations as needed.
The namespaces are reconstructed as "barrel"-style modules, which are identical to the old namespace objects in structure. These reconstructed namespaces are then imported in the newly module-ified files, making existing expressions like "ts." valid.
