[QNN EP] Add more op unit tests (fix Clip, TopK, Tile) (#17457)
### Description
Adds more operator unit tests (all op types should now have at least 1
unit test):
- [x] Reshape
- [x] Flatten
- [x] Squeeze
- [x] Unsqueeze
- [x] Gemm
- [x] Clip
- Enable QDQ Clip on HTP backend (when not optimized away by L1
ClipQuantFusion optimizer)
- Add support for 16-bit QDQ Clip to ClipQuantFusion optimizer
- [x] Split
- [x] Topk
- Enable QDQ TopK on HTP backend
- [x] Tile
- Enable QDQ Tile on HTP backend
### Motivation and Context
Increase QNN operator support and test coverage.