python: make DataFlowCall "publicly usable"

- add `getCallable`, `getArg` and `getNode`
- these are `none` for summary calls
- revert "external" uses (they had been changed to `DataFlowSourceCall`)

python/ql/test/experimental/dataflow/TestUtil/UnresolvedCalls.qll

@@ -12,8 +12,8 @@ class UnresolvedCallExpectations extends InlineExpectationsTest {
   override predicate hasActualResult(Location location, string element, string tag, string value) {
     exists(location.getFile().getRelativePath()) and
     exists(CallNode call |
-      not exists(DataFlowPrivate::DataFlowSourceCall dfc | dfc.getNode() = call |
-        // For every `CallNode`, there is a `DataFlowSourceCall` in the form of a `NonSpecialCall`.
+      not exists(DataFlowPrivate::DataFlowCall dfc | dfc.getNode() = call |
+        // For every `CallNode`, there is a `DataFlowCall` in the form of a `NonSpecialCall`.
         // It does not really count, as it has some abstract overrides. For instance, it does not
         // define `getCallable`, so checking for the existence of this guarantees that we are in a
         // properly resolved call.

python/ql/test/experimental/dataflow/calls/DataFlowCallTest.ql

@@ -15,7 +15,7 @@ class DataFlowCallTest extends InlineExpectationsTest {
 
   override predicate hasActualResult(Location location, string element, string tag, string value) {
     exists(location.getFile().getRelativePath()) and
-    exists(DataFlowSourceCall call |
+    exists(DataFlowCall call |
       location = call.getLocation() and
       element = call.toString()
     |

python/ql/test/experimental/dataflow/coverage/argumentRoutingTest.ql

@@ -22,7 +22,7 @@ class Argument1RoutingConfig extends DataFlow::Configuration {
   override predicate isSource(DataFlow::Node node) {
     node.(DataFlow::CfgNode).getNode().(NameNode).getId() = "arg1"
     or
-    exists(AssignmentDefinition def, DataFlowPrivate::DataFlowSourceCall call |
+    exists(AssignmentDefinition def, DataFlowPrivate::DataFlowCall call |
       def.getVariable() = node.(DataFlow::EssaNode).getVar() and
       def.getValue() = call.getNode() and
       call.getNode().(CallNode).getFunction().(NameNode).getId().matches("With\\_%")