Implement short-circuiting for assertions

[Schaeff]

currently

if c then foo() else bar() fi

would always panic if foo() panics (even if c in false)

This is because we inline foo(), and conditionally return its result, but if a panic happened in the statements of foo, it would happen even if this branch isn't executed.

With this change, panics in each branch lead to the whole execution panicking only if the given branch is "executed", ie if cis true.

Both branches are still technically being executed (and paid for in terms of constraints), but the behavior is closer to what would expect.

Todo:

• minimize constraints: next PR
• try to reduce what we can before flattening to benefit from boolean propagation: next PR
• tests nested conditionals
• fix indentation on display implementation
• put behind flag?

[dark64]

Compile config should be updated in the zokrates_js type definition file as well: https://github.com/Zokrates/ZoKrates/blob/conditional-panics/zokrates_js/index.d.ts#L14

[Schaeff]

Compile config should be updated in the zokrates_js type definition file as well: https://github.com/Zokrates/ZoKrates/blob/conditional-panics/zokrates_js/index.d.ts#L14

changed

[dark64]

LGTM!