[TS] Fix relative import paths of generated TypeScript code (#8880)

* Refactor logic that generates import paths in AddImport

* Add new tests to validate relative import path fix

* Generate goldens

* Generate example code

* Format TS generator file

* Revert "Format TS generator file"

This reverts commit 0f0b24aee9.

* Fix merge conflicts

---------

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

tests/ts/relative_imports/relative_imports.fbs

@@ -0,0 +1,20 @@
+namespace Transit.One;
+
+table Info {
+  timestamp:ulong;
+}
+
+namespace Transit.Two;
+
+table Identity {
+  id:uint;
+}
+
+namespace Transit.Three;
+
+table Header {
+  info:Transit.One.Info;
+  id:Transit.Two.Identity;
+}
+
+root_type Header;