Suggestion: add using fields to classes that are auto-disposed on @@dispose

[dead-claudia]

The idea is that this...

class C {
    using a = foo();
    using #b = bar();
    await using c = baz();
    await using #d = thing();
}

...is sugar for (roughly) this:

class C {
    a = foo();
    #b = bar();
    c = baz();
    #d = thing();

    [Symbol.dispose]() {
        try {
            this.a[Symbol.dispose]()
        } finally {
            this.#b[Symbol.dispose]()
        }
    }

    async [Symbol.asyncDispose]() {
        try {
            await this.c[Symbol.asyncDispose]()
        } finally {
            await this.#d[Symbol.asyncDispose]()
        }
    }
}

It'd make collections of named disposable things a lot easier to work with.

Obviously intended as a follow-on proposal, so feel free to label accordingly.