improve android instrumentation test and update README
Added tests for lite interpreter. By default the run_test.sh will use lite interpreter, unless manually set BUILD_LITE_INTERPRETER=0
Also fixed model generation script for android instrumentation test and README.
Verified test can pass for both full jit and lite interpreter. Also tested on emulator and real device using different abis.
Lite interpreter
```
./scripts/build_pytorch_android.sh x86
./android/run_tests.sh
```
Full JIT
```
BUILD_LITE_INTERPRETER=0 ./scripts/build_pytorch_android.sh x86
BUILD_LITE_INTERPRETER=0 ./android/run_tests.sh
```
Pull Request resolved: https://github.com/pytorch/pytorch/pull/72736
