1) Since we collect a stack trace for unhandled promises we might end up
invoking code right before the shutdown phase.
2) Any dynamic module import that happens in this phase will enqueue a
microtask job with a freshly allocated DynamicImportData object. It
only gets deleted when fully emptying the microtask queue.
3) Since we're exiting we might end up with a non-empty microtask queue.
4) LSAN detects this as a leak on shutdown.

To make LSAN happy again d8 now keeps track of DynamicImportData to
free them on destructing PerIsolateData.

Bug: chromium:1158223
Change-Id: I9bb21f71bffc75a0d5f4ffc5bf0727c7b4cbab88
Reviewed-on: https://chromium-review.googlesource.com/c/v8/v8/+/2599755
Commit-Queue: Camillo Bruni <cbruni@chromium.org>
Reviewed-by: Shu-yu Guo <syg@chromium.org>
Cr-Commit-Position: refs/heads/master@{#72008}