[mlir][python] Make DenseBoolArrayAttr.get work with list of bools.

This patch makes the getter function of `DenseBoolArrayAttr` work more
intuitively. Until now, it was implemented with a `std::vector<int>`
argument, which works in the typical situation where you call the pybind
function with a list of Python bools (like `[True, False]`). However, it
does *not* work if the elements of the list have to be cast to Bool
before (and that is the default behavior for lists of all other types).
The patch thus changes the signature to `std::vector<bool>`, which helps
pybind to make the function behave as expected for bools. The tests now
also contain a case where such a cast is happening. This also makes the
conversion of `DenseBoolArrayAttr` back to Python more intuitive:
instead of converting to `0` and `1`, the elements are now converted to
`False` and `True`.

Reviewed By: springerm

Differential Revision: https://reviews.llvm.org/D158973