Php file generators refactoring - model, resource model, collection, save entity command, etc.

[bohdan-harniuk]

Description (*)
What was done:

1. added PHP file generation abstract layer to avoid code duplication and extend the flexibility of PHP files generators
2. adjusted model generation
3. adjusted resource model generation
4. adjusted collection model generation
5. adjusted save entity command generation
6. adjusted abstract PHP file model to provide additional features to it
7. adjusted related to these changes files
8. updated branch to 3.2.0-develop
9. adjusted data provider class generation
10. fixed critical error in UiComponentFormGenerator class (for existed file generation)
11. fixed critical error in UiComponentGridXmlGenerator (for existed file generation)
12. adjusted delete entity controller file generation
13. adjusted new action entity controller file generator

Contribution checklist (*)

• Pull request has a meaningful description of its purpose
• All commits are accompanied by meaningful commit messages
• All new or changed code is covered with integration/functional tests (if applicable)
• All automated tests passed successfully (all builds are green)