Allow mutual interaction between source code and the trace graph

[laike9m]

Some ideas:

• When clicking/hovering on a trace graph node, highlight the corresponding text in the source code panel
• Vice versa

The difficult part is that if an identifer appears multiple times in the same line, we may not be able to tie them to the correct nodes accurately. But at least we could just highlight the whole line or all nodes in the same line, which is already useful.