Improve the readability of generated source code which contains `GetAbstractCobolField`.

[yutaro-sakamoto]

cobj convert some cobol source code to Java source code which uses a class GetAbstractCobolField.
The source code related to GetAbstractCobolField are a little difficult to read.

The followings are reproduction code and a compilation command.

a.cbl

       IDENTIFICATION    DIVISION.
       PROGRAM-ID.       a.
       DATA              DIVISION.
       WORKING-STORAGE   SECTION.
       01  XX         PIC N(5).
       PROCEDURE         DIVISION.
           DISPLAY XX(2:3).
           GOBACK.

the compilation command

cobj -debug a.cbl

a.java

          CobolTerminal.display (0, 1, 1, (new GetAbstractCobolField(){ public AbstractCobolField run() throws CobolStopRunException {           CobolUtil.cobCheckRefModNational (((b_I.getNumdisp(2) * 2) - 1), (b_J.getNumdisp(1) * 2), 10, str_1_X);
return CobolFieldFactory.makeCobolField((b_J.getNumdisp(1) * 2), b_588d8096da.getSubDataStorage((((b_I.getNumdisp(2) * 2) - 1) - 1)), a_1);}}).run());