#397: Rename invocation.toolExecutionSuccessful to executionSuccessful

Jim suggested this renaming
invocation.toolExecutionSuccessful  to  executionSuccessful , arguing that if in future we extend SARIF to represent dynamic analysis, we could reuse the  invocation  object to represent the launch of the program under test, in which case the thing whose execution was successful wouldn’t be the “tool”.

Michael and I agree with this renaming, and I made it directly in the provisional draft.

Thanks,
Larry