The stack chart's view for allocations data isn't finished

In a recent PR (https://github.com/firefox-devtools/profiler/pull/3308) I made the stack chart work for allocations data. However I noticed some issues:

* the tooltip still shows timing data -- I'm not even sure it is correct, it may be displaying allocation data with timing units...
* it's also possible that the stacks are incorrect, because I'm not sure the right thread/sample table objects are being used.

So in this issue we want to double check this.

[Here is an example profile](https://main--perf-html.netlify.app/public/1d3ekymrdk1b2qkwe2gyvn9mzwdmamkkqvw35v8/stack-chart/?ctSummary=native-deallocations-memory&globalTrackOrder=0-1-2-3-4-5-6-7-8-9&hiddenGlobalTracks=1-2-3-4-5-6-8&hiddenLocalTracksByPid=31597-0-2-4-6~32136-0&localTrackOrderByPid=31597-7-8-0-1-2-3-4-5-6~20939-0~31653-0~11801-0~31835-0~12044-0~31844-0~31742-0~32136-1-0~4276-0-1~&thread=0&timelineType=cpu-category&v=5)

┆Issue is synchronized with this [Jira Task](https://mozilla-hub.atlassian.net/browse/FP-391)