[move-prover] parenthesis the ITE expression when translating to boogie

This is motivated by the following expression generated by the spec
simplifier, which causes a type error in Boogie (but no type error in
our AST):

```boogie
(x > 0) && if (true) then (0) else (1) >= 0;
```

In this case, Boogie complains that the then-else branches return
different types which is int (for the then branch) and bool (for the
else branch).

This is caused by the fact that the ITE expression itself is not
enclosed in a parenthesis. The correct encoding should be:

```boogie
(x > 0) && (if (true) then (0) else (1)) >= 0;
```

This commit fixes this issue by wrapping the ITE expression with ().

Closes: #9686

language/move-prover/boogie-backend/src/spec_translator.rs

@@ -583,12 +583,15 @@ impl<'env> SpecTranslator<'env> {
             }
             ExpData::IfElse(node_id, cond, on_true, on_false) => {
                 self.set_writer_location(*node_id);
-                emit!(self.writer, "if (");
-                self.translate_exp(cond);
-                emit!(self.writer, ") then ");
+                // The whole ITE is one expression so we wrap it with a parenthesis
+                emit!(self.writer, "(");
+                emit!(self.writer, "if ");
+                self.translate_exp_parenthesised(cond);
+                emit!(self.writer, " then ");
                 self.translate_exp_parenthesised(on_true);
                 emit!(self.writer, " else ");
                 self.translate_exp_parenthesised(on_false);
+                emit!(self.writer, ")");
             }
             ExpData::Invalid(_) => panic!("unexpected error expression"),
         }