Implement Hit Condition UI for breakpoints

[weinand]

SourceBreakpoints and FunctionBreakpoints support an optional hitCondition attribute which controls how many time a breakpoint has to be hit in order to 'break' execution.
Since a debug adapter is free to decide what kind of hit expressions to accept, the hitCondition is of type string.
This makes the attribute very similar to the already existing condition attribute of the breakpoint types and suggests that the UI for editing this new attribute aligns with the UI for editing breakpoint conditions.

The corresponding debug protocol addition: microsoft/vscode-debugadapter-node#37
And the implementation for node-debug: #12374

[isidorn]

Fixed via 134a1ec

[isidorn]

@weinand This is done for regular breakpoints. We have an open question on what to do for function breakpoints - since they do not have a representation in the editor. So far we have also not exposed in the ui how to add a regular condition for function breakpoints.
There are a couple of options:

• somehow we start representing function breakpoints in the editor gutter - thus specifying the condition / hit count is the same as for regular breakpoints
• we add context menu actions in the breakpoints pane for editing a function breakpoint, this actions could then trigger the same experience as for regular breakpoints - though where to render the widget now - since function breakpoints have no line number
• add context menu acitons in breakpoint pane which would just open a native electron input box for specifying the condition, and another one for specifying the hit count

Let me know what you think