tools: enable no-unsafe-optional-chaining lint rule

This rule is new in ESLint 7.15.0.

.eslintrc.js

@@ -234,6 +234,7 @@ module.exports = {
     'no-unreachable': 'error',
     'no-unsafe-finally': 'error',
     'no-unsafe-negation': 'error',
+    'no-unsafe-optional-chaining': 'error',
     'no-unused-expressions': ['error', { allowShortCircuit: true }],
     'no-unused-labels': 'error',
     'no-unused-vars': ['error', { args: 'none', caughtErrors: 'all' }],