Update on "[llama-mm] Add export-friendly tile position embedding"

Summary:

Before we make a decision on whether torchtune takes this
export-friendly version of `TilePositionEmbedding`, we put it under
`extension/llm` so that users can start to use it.

Added unit tests to make sure the behavior is the same as the reference
implementation in torchtune and export/AOTI/ET all working properly.

Test Plan:

Reviewers:

Subscribers:

Tasks:

Tags:

[ghstack-poisoned]

Author: larryliu0820

pytest.ini

@@ -38,6 +38,7 @@ addopts =
     # backends/xnnpack
     backends/xnnpack/test
     # extension/
+    extension/llm/modules/test
     extension/pybindings/test
     # Runtime
     runtime