Evaluate doesn't correctly handle assignments to locals

[rmacnak-google]

Pulling a more specific problem out of #23446,

main() {
   var x = 1;
   debugger();  // evaluate `x++`, continue
   print(x);
}

This should print 2, but currently will print 1. The current compilation strategy for evaluate is roughly to create a new closure function (var x) => x++, which fails to write back to frame we're evaluating in. Squeak Smalltalk and Newspeak instead do something like (var context) => context[0] = context[0] + 1), where context is the reified activation record and x was allocated to slot 0, which makes the evaluation have the expected effect.

[a-siva]

//cc @derekxu16