Allow documentation of autoloads with GDScript documentation comments

[Pennycook]

I use GDScript documentation comments extensively for my editor plugins. Unless I'm mistaken, classes only show up in the "Search Help" list if they've been defined with class_name, which makes it difficult to document the behavior of autoload singletons. Attempting to define an autoload with the same name as a class results in an error.

The way I'm currently working around this is to define separate (but related) names: I have a class called InputPromptManager which documents that it is autoloaded under the name PromptManager. Although this works, it's not very satisfying, as the behavior is different from built-in singletons (like InputMap).

I'm not sure what it would take to make this work, but ideally I'd like an entry for each autoloaded class to show up in the "Search Help" list.

[dalexeev]

• See also Facilitate class documentation of project singletons (or, allow hyperlinks to class docs using arbitrary text) #8441.