[diff flame graph view] Consider bringing back the split view

[grafakus]

Feature description

Is your feature request related to a problem? Please describe.

The previous version of the app offered a "Comparison view", where the baseline and the comparison each had their own flame graph:

Describe the solution you'd like

Consider adding this layout, as it can be useful for some users to compare two flame graphs side by side instead of a single diff flame graph.

It could be done by adding radio buttons in the UI to allow the user to switch between the 2 layouts.

Alternatives considered

Describe alternatives you've considered

Keeping the current diff view, as it is, with a diff flame graph.

Additional context

Idea received during an internal feedback interview.

[grafakus]

cc @adamquan