f0bdf2a1ae
Mutable exports, i.e. using this pattern
```
export let x = 0;
export function f() {
x += 1;
}
```
is problematic to transpile to CommonJS and Goog.module systems, we are
working on banning it google internal codebase.
The workaround is adding an explcit getter function.
PR Close #32425