Provide a way to collapse non-branching call nodes in call tree

[gregtatum]

Looking at a call tree like this is kind of unhelpful, as it doesn't show anything pertinent that is going on. It would be useful to be able to collapse non-branching call nodes in a call tree. This could be implemented as a view on the call tree, so that it could be toggleable and not affect the call tree transforms.

I'm not sure the best way to represent the collapse. Unbranched paths could have First Function [...] Last Function as a row, and you could click the [...] button in order to uncollapse it.

Or maybe something like:

However it's implemented, this could probably be done in the CallTree component UI, maybe with a new intermediate data structure.

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