feat!: turn on noUncheckedIndexedAccess for libraries

See https://www.semver-ts.org/formal-spec/5-compiler-considerations.html#strictness
for the arguments for turning on noUncheckedIndexedAccess for libraries.

In short, it helps prevent shipping accidental breaking type changes to
library consumers.

(Note the link also suggests turning on `exactOptionalPropertyTypes`,
but I still have doubts about it, as it would not be helpful without
a specific coding style, which is hard to enforce.)

Author: haoqunjiang

tsconfig.lib.json

@@ -8,6 +8,8 @@
     // Libraries generally require more strict type accuracy.
     // For example, its types must be compatible with the Vue types.
     // So we don't want to skip the type checking of its dependencies.
-    "skipLibCheck": false
+    "skipLibCheck": false,
+
+    "noUncheckedIndexedAccess": true
   }
 }