[TS] Fix relative paths for exports (#8517)

Fixes an issue where exports were using incorrect relative paths for
>=3 namespace levels. This is fixed by making the starting range of the
namespace components relative to the amount of components.

Co-authored-by: Björn Harrtell <bjornharrtell@users.noreply.github.com>

tests/ts/longer-namespace/a/b/c.js

@@ -0,0 +1,3 @@
+// automatically generated by the FlatBuffers compiler, do not modify
+/* eslint-disable @typescript-eslint/no-unused-vars, @typescript-eslint/no-explicit-any, @typescript-eslint/no-non-null-assertion */
+export { Person } from './c/person.js';