Support more unwind nodes

[giltho]

PRs #682 and #700 respectively make call a terminator and add a reference to the unwinding block in ULLBC.

This process needs to be done again for the following ULLBC statements which are terminators in MIR and have unwind blocks:

• [ ] Drop
• [ ] Assert

(I realised I changed context and never noted anywhere that this wasn't finished.)

[Nadrieril]

Indeed! Thanks for writing this down.

And correspondingly in llbc these statements should get an extra unwind: Block field. Note that for Assert this may require updating some of our reconstruction passes; if anyone wants to tackle this issue don't hesitate to ask for help on that.

[Nadrieril]

Drop was done in #893!