Bugfix/ls24003755/ds to string when ds is greater than string

[davidepalladino-apuliasoft]

Description

This work fixes the assignment of DS content to an element of array which is String with size smaller than DS.
Under the hood has been removed restriction of size, by considering that RPG truncates the DS content if the target is smaller than source, in this case a String. Then, has been applied the fix with an important refactoring of code, by using when construct. If the target is StringType, performs the right padding or truncating based of size and varying flag. For truncating, the unused method setSubstring has been refactored for the purpose.
Finally, the two simple RPG programs for tests has been developed and executed on AS400.

Related to #LS24003755

Checklist:

• There are tests regarding this feature
• The code follows the Kotlin conventions (run ./gradlew ktlintCheck)
• The code passes all tests (run ./gradlew check)
• There is a specific documentation in the docs directory

[lanarimarco]

The tests are a little bit complex, making it really difficult for me to understand their purpose. Please simplify them by focusing on the essential aspects or by adding comments. Always keep in mind that a good unit test should be understandable within a few seconds, without requiring knowledge of the entire context.

[davidepalladino-apuliasoft]

The tests are a little bit complex, making it really difficult for me to understand their purpose. Please simplify them by focusing on the essential aspects or by adding comments. Always keep in mind that a good unit test should be understandable within a few seconds, without requiring knowledge of the entire context.

I added an high level comment to program RPG. The program is similar to original case:

• by changing the name of variables with clear names;
• by populating each field with a proper substring of Lorem ipsum....