Move ExecuTorchDemo Android app to pytorch-labs/executorch-demo

[mergennachin]

Follow-up to #8627

Migrate https://github.com/pytorch/executorch/tree/main/examples/demo-apps/android/ExecuTorchDemo to https://github.com/pytorch-labs/executorch-examples

cc @iseeyuan @lucylq @helunwencser @tarun292 @kimishpatel @jackzhxng @kirklandsign @cbilgin @byjlw

[kirklandsign]

I plan to do it in a few steps:

• 1. Copy it first, and modify it to use prebuilt AAR instead of building jar/so. This means we can't use QNN because we don't have a prebuilt AAR with QNN enabled.
• 2. Build and upload AAR with QNN
• 3. Remove old codebase
• 4. Update all docs

Also
[] refactor the code about pte and jpg resources