Test setting variable values

[isidorn]

Tests #7744:

• any platform - @sandy081

During a debugging session it is now possible to change a value of any primitive variable (leafs in the variable tree). Currently this is only supported in node-debug. The accepted syntax is the same as for watch expressions and the REPL.

Verify:

• you can use the context menu / double click to change the value of any primitive variable; this includes object properties and individual array entries,
• changing it to some invalid value clearly shows the error
• try to be creative and break it

[sandy081]

Tested. Tried to break it but can't :). Looks good.

[isidorn]

Great - thanks! Then we can close this issue