This PR does
- fix some bugs to support masked load/store,
- refine frontend, and support the `and` and `or` syntax in mask(by
extending the BoolOp in python ast.visitor), e.g. `tl.store(...,
mask=offset<n and other_conditions)`,
- add `arith.cmpI` and `arith.cmpF` op conversion in backend(required by
mask),
- add more test cases in vecadd.