Emit nested expando function assignments in declarations

[Copilot]

Declaration emit only serialized expando function properties assigned as top-level expression statements. Assignments in initializers or blocks were bound but dropped from the generated namespace.

• Declaration emit

  • Emit expando properties from the function declaration’s collected symbol properties.
  • Suppress duplicate namespace emission from assignment statements already covered by the function-level emit.
  • Preserve synthesized multi-statement output when replacing declarations.

• Code actions

  • Deduplicate identical isolated-declaration expando namespace fixes across diagnostics.

• Regression coverage

  • Added compiler coverage for expando assignments in a variable initializer and block.

function Foo(): void {}
Foo.top = 1;
let d: number = (Foo.inInitializer = 2);
if (true) {
    Foo.inBlock = 3;
}

now emits:

declare function Foo(): void;
declare namespace Foo {
    var top: number;
    var inInitializer: number;
    var inBlock: number;
}
declare let d: number;

[hkleungai]

Just curious, is this PR also solving the issue I raised in #4045? If not, also fine :)