Provide a way to explicitly invoke the debugger (#34006)

* Provide a way to explicitly invoke the debugger with in the debug strategy

* Merge the debugger strategy into StrategyBase

* Fix some logic, pin to a single result

* Make redo also continue

* Make sure that if the debug closure doesn't need to process the result, that we still return it

* Fix failing tests for the strategy

* Clean up messages from debugger and exit code to match bin/ansible

* Move the FieldAttribute higher, to apply at different levels

* make debugger a string, expand logic

* Better host state rollbacks

* More explicit debugger prompt

* ENABLE_TASK_DEBUGGER should be boolean, and better docs

* No bare except, add pprint, alias h, vars to task_vars

* _validate_debugger can ignore non-string, that can be caught later

* Address issue if there were no previous tasks/state, and use the correct key

* Update docs for changes to the debugger

* Guard against a stat going negative through use of decrement

* Add a few notes about using the debugger on the free strategy

* Add changelog entry for task debugger

* Add a few versionadded indicators and a note about vars -> task_vars

lib/ansible/executor/stats.py

@@ -46,6 +46,16 @@ class AggregateStats:
         prev = (getattr(self, what)).get(host, 0)
         getattr(self, what)[host] = prev + 1
 
+    def decrement(self, what, host):
+        _what = getattr(self, what)
+        try:
+            if _what[host] - 1 < 0:
+                # This should never happen, but let's be safe
+                raise KeyError("Don't be so negative")
+            _what[host] -= 1
+        except KeyError:
+            _what[host] = 0
+
     def summarize(self, host):
         ''' return information about a particular host '''