Inspector: clear the done flag when revisiting node

[grg]

Set the done flag to false when revisiting a node in Tracker::try_start. Fixes a small regression introduced in #4447.

Without this fix, a Tofino pass errors out with an assertion failure from the Visitor infrastructure: Assertion current.depth < 10000' failed.` Without resetting the done flag in the tracker, the Inspector::apply_visitor method will always follow the "New or Revisit" path instead of the "Busy" path after a node has been visited once.

The associated test program mimics the Tofino pass that shows the problem.

[asl]

@grg I think the code is similar here as with Visitor::ChangeTracker. Does it also have the same problem? Looks like Visitor::ChangeTracker::try_start is pretty much the same. However, it seems that it uses slightly different set of flags...

[grg]

@grg I think the code is similar here as with Visitor::ChangeTracker. Does it also have the same problem? Looks like Visitor::ChangeTracker::try_start is pretty much the same. However, it seems that it uses slightly different set of flags...

I've now applied the fix to Visitor::ChangeTracker::try_start after creating a second test case for Modifier and seeing the same issue. The issue existed with Modifier/Transform even before the refactoring in #4447, but no one must have encountered it.

I also took the opportunity to simplify the test case slightly. My original submission enabled joinFlows and used the ControlFlowVisitor, but experimentation showed that neither was necessary to hit the issue.

[asl]

Awesome, thanks!