explicit-failing-assertions.feat

Code actions in editor to explicit failing assertions.
In VSCode, place the cursor on a failing assertion that support being made explicit and either
- Position the caret on a failing assertion, press CTRL+; and then ENTER
- Hover over the failing division by zero, click "quick fix", press ENTER
Both scenarios will explicit the failing assertion.
If you don't see a quick fix, it means that the assertion cannot be automatically made explicit for now.

Here is a initial list of assertions that can now be made explicit:
- Division by zero
- "out of bound" on sequences index, sequence slices, or array index
- "Not in domain" on maps
- "Could not prove unicity" of `var x :| ...` statement  
- "Could not prove existence" of `var x :| ...` statement