Refactor plugin.gd for improved readability and maintainability

[Miisan-png]

This commit includes several changes to improve the readability and maintainability of the plugin.gd file:

1. More descriptive comments have been added to provide better context for the code.
2. Repeated code checking the existence of editor_view and editor_view.editors_manager has been moved into a helper function _editor_view_and_manager_exist().
3. String literals that were used multiple times in the code have been replaced with constants to avoid magic strings and make future changes easier.

[Jowan-Spooner]

Thanks. I like the majority of these changes.

But:

• Documentation strings should start with ##

• Methods should be separated with two empty lines

• I would keep the sections, although they should be replaced with the new code regions. This is a personal preference, but I like to visualy indicate code that belongs together, I find it easier for navigation especially in long files.

• You seem to be using spaces instead of tabs. This is not a big deal, but a bit annoying, as we've used tabs across the whole project.

Edit: Additionally

• I would prefer to keep the short description at the top of the file. We've added those on many files to make it easier for new-comers scanning the plugins to understand the purpose of each file.

[Jowan-Spooner]

Btw, if you intend to do more PR's, feel free to join emilios discord where most of the developement discussion happens.

[Miisan-png]

Thanks, sure i will do that.