Currently when building a package on Windows, the typings re-export for secondary entry-points is not valid TypeScript. Similarly the metadata and the "package.json" files use non-posix paths and cause inconsistency within the NPM package.
For example:
_package.json_
```
"esm5": "./esm5\\core.js",
"esm2015": "./esm2015\\core.js",
```
_testing.d.t.s_ (of the `core` package)
```
export * from './testing\testing';
```
PR Close#27829
4caf6540d1