Add model files support for android tokenizer (#5727)

Summary:
Pull Request resolved: https://github.com/pytorch/executorch/pull/5727

Add model files support for android tokenizer. Previously we only support .bin files, but since the runner also supports .model now, updating the app side logic to allow .model tokenizer files.

Reviewed By: larryliu0820

Differential Revision: D63491811

fbshipit-source-id: b01ca836798794cbd0b0b377aa096a5c61a8f715