Make python statements available in the kernel

[1e-to]

The kernel function currently silently ignores Python exceptions and assertions.

• The raise statement
• The assert statement

It is the correct behavior as a kernel cannot have exception and assertion errors raised during execution. Thus, a proper user experience will be to raise an exception during lowering of a kernel if the kernel has either a raise or an assert.

[diptorupd]

To implement the feature the DpexCallConv used by the DpexKernelTarget should override we have to override return_user_exc to raise errors at compile-time.

[chudur-budur]

Solved by #1244

Looks like we need to silently ignore the assert and raise statements in kernel. Overloading return_user_exc will cause to fail different python expressions inside kernel, like range and %, because the numba lowering mechanism of these expressions throw exceptions in different places.