Debug Protocol: support 'restart frame'

[weinand]

Add protocol support for a restartFrame request.
A single argument frameId specifies the frame to restart.

[DavidKarlas]

This is similar to #28?
Maybe it could be merged into one command with addition of optional frame index parameter?
It might be confusing having two very similar commands unless I misunderstand this command...

[weinand]

@DavidKarlas good idea, I will consider your suggestion.
For now I have already added the restartFrame to the protocol, but the 1.11 version of the protocol is only a preview until the end of the sprint.

[weinand]

@DavidKarlas I've tried to merge 'restartFrame' into the 'setNextStatement' proposed in #28 but in the end I gave up because supporting different kinds of parameters (frameId vs. source location) on 'setNextStatement' was just adding complexity without gaining much: the UI for 'setNextStatement' is quite different from 'restartFrame'. The former works on individual statements in the source, the latter is more useful on call stack frames. So typically there is no shared code that has to deal with both cases.