Add instruction count column to Functions window

[gemesa]

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

I would like to be able to see the instruction count as a column in the functions window.

Describe the solution you'd like

See above.

Describe alternatives you've considered

Calculate/count it myself. It is simple on architectures with fixed size instructions but annoying on others, e.g. x86.

Additional context
N/A