[Task]: Require locks when assigning to a field of an isolated object in the init method after all the fields have been initialized

[MaryamZi]

Description

With the fix (#40757) for #40736, we will be making it an error when self of an isolated object is accessed outside a lock statement other than to set a value for a field.

But according to the spec, once all the fields are initialized, even subsequent assignments to fields need to happen within lock statements.

Given that not using locks here won't cause any correctness issues (since we require isolated expression when assigning anyway) and the task re-prioritization along with the extent of changes required (need to duplicate dataflow analyzer-like logic and address issues in the existing logic), we have deferred this for now.

Describe your task(s)

isolated class Foo {
    private int[][] x;

    isolated function init(int[][] x, int[] y) {
        self.x = x.clone(); // OK

        self.x.push(y); // error now because outside lock

        // Should also be an error according to the spec
        self.x = x.clone();
    }
}

Related area

-> Compilation

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