When searching the typings program for a package for imports a
distinction is drawn between missing entry-points and deep imports.
Previously in the `DtsDependencyHost` these deep imports may be
marked as missing if there was no typings file at the deep import path.
Instead there may be a javascript file instead. In practice this means
the import is "deep" and not "missing".
Now the `DtsDependencyHost` will also consider `.js` files when checking
for deep-imports, and it will also look inside `@types/...` for a suitable
deep-imported typings file.
Fixes#34720
PR Close#34695
Pete Bacon Darwin