Add prettier method to API

[javihern98]

Overview

We would like to add the Prettier method to the vtlengine library. The main goal is to migrate from the old engine the prettier method based on the AST Template.

Tasks to perform

• Generate the prettier method at API. The input will be a vtl script and the output will be the same vtl script, but formatted:

def prettier(script: str) -> str:
    ....

• Generate an internal function called stringify and a AST Template method called ASTStringify that will take the AST Object and it will extract the string representation. This string representation will include as well all children, and perform indentation where needed.
• Add some tests with unformatted code and formatted code

Important

This is a hard requisite for #67

How do we pretty up code

• We leave a space between each token
• We leave a blank line between each transformation
• On complex operators (like aggregation, analytic, joins), we open the ( and jump to the next line, adding some indentation (4 spaces or tab). We fill the code and close the )
• On clause operators, we jump to the next line before adding the [ and jump another line and adding indentation. We here fill each clause on each line and jump another line to close the operator with ]

Examples of pretty code