Place and route graphical breakpoints updates

[vaughnbetz]

Expected Behaviour

route_net_id >= 0 crashes with an unknown expression error if route_net_id is misspelt (e.g. route_net_ids)..

• should give an error message and proceed if we can't parse a formula, instead of crashing

Setting a router breakpoint every N iterations leads to next stopping after every net

• Should just stop next time a breakpoint condition is met, which is at the start of that routing iteration

route_net_id is misspelt in the pop-up when you stop (fix text)

[haydar-c]

Closing as solved in #3286