[mlir][async] Avoid crash when not using `func.func` (#72801)

The `createParallelComputeFunction` crashed when calling
`getFunctionTypeAttrName` during the creation of a new `FuncOp` inside
the pass. The problem is that `getFunctionTypeAttrName` looks up the
attribute name for the function type which in this case is `func.func`.
However, `name.getAttributeNames()` was empty when clients used
`llvm.func` instead of `func.func`.

To fix this, the `func` dialect is now registered as a dependent
dialect. Also, I've added an assertion which could save other people
some time.

Fixes #71281, fixes #64326.