Support thread-aware Profile.tree! on 1.8

[jpsamaroo]

Adapts to changes in JuliaLang/julia#41742, and requires JuliaLang/julia#42162

[jpsamaroo]

Aside: This supports indirect usage of FlameGraphs by Dagger through ProfileSVG, which doesn't appear to need any changes to account for the MT profiling changes.

[codecov]

Codecov Report

Merging #42 (96da799) into master (92bb8d7) will decrease coverage by 2.57%.
The diff coverage is 66.66%.

@@            Coverage Diff             @@
##           master      #42      +/-   ##
==========================================
- Coverage   93.65%   91.07%   -2.58%     
==========================================
  Files           5        5              
  Lines         268      269       +1     
==========================================
- Hits          251      245       -6     
- Misses         17       24       +7     

Impacted Files	Coverage Δ
src/graph.jl	93.61% <66.66%> (-0.95%)	⬇️
src/FlameGraphs.jl	0.00% <0.00%> (-46.67%)	⬇️

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[timholy]

I guess this will fail nightly until the 2nd PR is merged. If I don't notice, feel free to ping me, @jpsamaroo. Thanks for doing this!

[jpsamaroo]

I think we can wait for the Julia PR to be merged first so we don't mess up CI. It gives me a bit more time to test this with Dagger and make sure I didn't miss anything.

[timholy]

This doesn't pass but it's a step in the right direction. Let's merge it and move to the next issue.