src/vs/base/common/resources.ts/ExtUri/resolvePath
class ExtUri:	resolvePath(base: URI, path: string): URI {
		if (base.scheme === Schemas.file) {
			const newURI = URI.file(paths.resolve(originalFSPath(base), path));
			return base.with({
				authority: newURI.authority,
				path: newURI.path
			});
		}
		path = extpath.toPosixPath(path); // we allow path to be a windows path
		return base.with({
			path: paths.posix.resolve(base.path, path)
		});
	}