Merge pull request #12952 from michaelnebel/csharp/refactorcontentflow

C#: Re-factor ContentFlow to a parameterised module and use the new API.

Author: michaelnebel

config/identical-files.json

@@ -40,7 +40,6 @@
     "csharp/ql/lib/semmle/code/csharp/dataflow/internal/DataFlowImpl3.qll",
     "csharp/ql/lib/semmle/code/csharp/dataflow/internal/DataFlowImpl4.qll",
     "csharp/ql/lib/semmle/code/csharp/dataflow/internal/DataFlowImpl5.qll",
-    "csharp/ql/lib/semmle/code/csharp/dataflow/internal/DataFlowImplForContentDataFlow.qll",
     "go/ql/lib/semmle/go/dataflow/internal/DataFlowImpl1.qll",
     "go/ql/lib/semmle/go/dataflow/internal/DataFlowImpl2.qll",
     "go/ql/lib/semmle/go/dataflow/internal/DataFlowImplForStringsNewReplacer.qll",