gh-138122: Add docs button to Tachyon heatmap and flamegraph

[StanFromIreland]

I have also converted it to use SVG's from bootstrap icons, I can revert back to characters if you prefer. This is because I had difficulties with the characters, it was difficult to align them, e.g. it ended up looking like this:

With SVG's, we have more control over how it renders, with this PR:

And, this PR also introduces a new docs (book) button that links to:

https://docs.python.org/PYTHON_VERSION_USED/library/profiling.sampling.html 

• Issue: Implement PEP 799 – A dedicated profiling package for organizing Python profiling tools #138122

[pablogsal]

Amazing work sir!