Hide private func and variables in editor

[xDGameStudios]

Issue description:
This is more a suggestion and not a bug. We all know that all funcs and variables are public in godot, but it would be great if we could hide wanted funcs and vars from autocomplete from outside the script. For example:

`#my_class.gd
class_name MyClass

var public_var
hide var _private_var
`

`#my_refering_class.gd

var instance:MyClass
`

when refering to instance in the second file I won't get auto-completion for the hidden variables only the non hidden (kinda like a public private but only for auto completion this could work also with funcs)

[Zylann]

I though these would inherently never popup because they start with _ and I never write something._ :s It's weird that they would still appear (as long as you don't type ._ of course), and if they do, they would likely be the last suggestions since _ is not a letter?

Otherwise that could be yet another one for #20318, unless there is a consensus to consider ._xxx to be understood by autocomplete and hidden de facto.

Notes:

• _ doesn't differentiate the private and protected OOP terms
• There are cases where we do self.xxx
• Also .xxx() to call base functions

[xDGameStudios]

That could also be an option "_" be considered automatically as hidden... when making a base class
for example DataGrid, that has some arrays and some public functions, I don't want the end user to access the underlying array properties for example. I understand that he may be able to access them anyway but at least it doesn't come in the autocomplete..

[clayjohn]

Feature and improvement proposals for the Godot Engine are now being discussed and reviewed in a dedicated Godot Improvement Proposals (GIP) (godotengine/godot-proposals) issue tracker. The GIP tracker has a detailed issue template designed so that proposals include all the relevant information to start a productive discussion and help the community assess the validity of the proposal for the engine.

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