[flamegraph] Visualize when there's inlining happening between two nodes in a flamegraph

[simonswine]

Feature description

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

When one or more functions are inlined into its caller, the upstream flamegraph of pprof shows this by not displaying a border between two nodes:

So in this example:

• (*Mutex).Unlock inlined into (*RWMutex).Unlock
• (*Mutex).Lock inlined into(*RWMutex).Lock

We currently show this like this:

Describe the solution you'd like

I think we should consider following the example of pprof