Add dts bundling

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.

src/compiler/program.ts

@@ -230,7 +230,7 @@ export function createCompilerHostWorker(options: CompilerOptions, setParentNode
 }
 
 /** @internal */
-interface CompilerHostLikeForCache {
+export interface CompilerHostLikeForCache {
     fileExists(fileName: string): boolean;
     readFile(fileName: string, encoding?: string): string | undefined;
     directoryExists?(directory: string): boolean;
@@ -4358,7 +4358,7 @@ export function filterSemanticDiagnostics(diagnostic: readonly Diagnostic[], opt
 }
 
 /** @internal */
-interface CompilerHostLike {
+export interface CompilerHostLike {
     useCaseSensitiveFileNames(): boolean;
     getCurrentDirectory(): string;
     fileExists(fileName: string): boolean;