Improve FILLER recognition in InsertVariableDisplay

[fm-117]

InsertVariableDisplay does not use IsFiller() extension method to identify FILLERs among data definitions. To help distinguish between real FILLERs and anonymous data, we should use this method.

[fm-117]

       IDENTIFICATION DIVISION.
       PROGRAM-ID. TCOMFL06.
       DATA DIVISION.
       WORKING-STORAGE SECTION.
       01 auto-select.
          05.
             10 PIC X(8).
             10 PIC X(5).
             10 PIC X(3).
       PROCEDURE DIVISION.
           GOBACK
           .
       END PROGRAM TCOMFL06.
-------------------------------------------------------------------------------------------------
TypeCobol.LanguageServer.Commands.InsertVariableDisplay.InsertVariableDisplayRefactoringProcessor
-------------------------------------------------------------------------------------------------
[
    {
        "textDocument": { "uri": "file:/test.expected.cbl" },
        "position": { "line": 9, "character": 26 }
    },
    false,
    {
        "vm": 1, "idx": 0, "ch": [
            {
                "vm": 2, "name": "auto-select"
            }
        ]
    }
]

The value of the whole 05 or individual 10 won't be displayed because in automatic mode we don't visit FILLERs.

[fm-117]

What is fixed:

• Adressing the first FILLER of a group is now done correctly, previously InsertVariableDisplay would display the value of the whole parent group
• When using automatic selection, FILLERs are defined the same way as in AdjustFillers, this allows to display data nested under anonymous levels properly

What remains unfixed:

• Autoselecting a group having only anonymous children won't give any value in generated DISPLAYs.