compiler: drop with objects at a loop's continue landing

[nooga]

Closes the FIXME left by #719.

Problem: a continue that leaves a with body through a finally keeps the with objects enclosing the try pushed, so the finally body can still see them. Nothing dropped them afterwards, so they stayed in scope for the next iteration. A lookup inside a later with in that iteration then resolved through the leaked object:

var o = { x: "leak" }, x = "out";
for (var i = 0; i < 2; i++) {
  with ({}) seen.push(x);   // second iteration saw "leak"
  with (o) { try { continue; } finally {} }
}

Fix: each loop (while, for, do-while, for-in, for-of) now emits OpTruncateWith at its continue landing, as it already does at its break landing. Normal fall-through reaches the landing with nothing extra pushed, so the truncate is a no-op there. It is only emitted when the loop body contains a with.

Testing

• New smoke test tests/scripts/with_continue_through_finally.ts. TestScripts is green.
• A probe covering all five loop kinds leaked on main and passes with this change.
• test262 (language + built-ins, vs main): no change. No test262 test covers this case.

🤖 Generated with Claude Code