treeshake bug: object spread side effects incorrectly dropped

[kzc]

• Rollup Version: rollup v2.50.0
• Operating System (or Browser): n/a
• Node Version (if applicable): n/a

Repro

$ cat object-spread-effects.js
let result = "FAIL";
const unused = ({
    ...{
        get prop() {
            result = "PASS";
        }
    }
});
console.log(result);

Expected Behavior

$ cat object-spread-effects.js | node
PASS

Actual Behavior

$ cat object-spread-effects.js | rollup --silent | node
FAIL

$ cat object-spread-effects.js | rollup --silent
let result = "FAIL";
console.log(result);

[lukastaegert]

Fix at #4113