[Major] Update to LLVM 19.1 and merge MLIR dialect

[chhzh123]

Description

This PR is a significant change for Allo:

1. Update the LLVM version from 18.1 to 19.1.
2. Merge the hcl-dialect to this repo to reduce the maintenance burden.
3. Update all HeteroCL-related naming to Allo.
4. Integrate all the build processes in setup.py, so users can directly call pip install . to install Allo without setting up the MLIR dialect first.
5. Create a new docker named chhzh123/allo:llvm-19.x-py3.12 and update CI.
6. Update documents to depict the latest changes.

Checklist

• PR's title starts with a category (e.g. [Bugfix], [IR], [Builder], etc)
• Changes are complete (i.e. I finished coding on this PR)
• All changes have test coverage (It would be better to provide ~2 different test cases to test the robustness of your code)
• Code is well-documented