Improve "Making Plugins" documentation

[Hpmason]

Your Godot version: 3.4

Issue description: Making plugins documentation is a bit confusing in some parts and has inconsistencies between the two examples.

Confusing:

• End of the first example links to the bottom of the page to check the results. That explains how to check the results of the dock, to me it made it seem like the button example will show up in a dock, not a node resource. I think this would greatly benefit with more instructions and pictures on how to check the button example.

Inconsistencies:

1. Methods for initially creating plugins are different

   • Button example uses Godot dialog to create plugin files
   • Custom Dock example manually creates the files (Not easily done in the Godot file explorer)

2. Values for creating plugins are different:

   • Button

     Plugin Name: My Custom Node
     Subfolder: my_custom_node
     Description: A custom node made to extend the Godot Engine.
     Author: Your Name Here
     Version: 1.0.0
     Language: GDScript
     Script Name: custom_node.gd
     Activate now: No

   • Dock (with [plugin] header)

     name="My Custom Dock"
     description="A custom dock made so I can learn how to make plugins."
     author="Your Name Here"
     version="1.0"
     script="custom_dock.gd"

Some of these confusions could just be me and they're not a huge deal, but I think it'd be helpful to clarify some of these things.

URL to the documentation page (if already existing): https://docs.godotengine.org/en/stable/tutorials/plugins/editor/making_plugins.html

https://github.com/godotengine/godot-docs/blob/master/tutorials/plugins/editor/making_plugins.rst

[Hpmason]

I've found similar inconsistencies between the "Making Plugins" tutorial and the "Spatial gizmo plugins" tutorial.

Between the two tutorials:

• Naming conventions are different (files and folder names use different casing between tutorials) snake_case vs PascalCase vs kebab-case
• preload() path absolute vs relative path
• File name in comments at the very beginning of code examples for most Gizmo tutorial examples (not all of them)

Confusing (Gizmo tutorial):

• Could use images on where to find gizmos
  • I can't seem to find page specifically for gizmos in the docs, so i think it'd be helpful to show images and examples
• "Simple Approach" and "Alternative approach" uses a file MyCustomSpatial.gd which is not shown/mentioned else where

I also think it'd be helpful to post these as full examples somewhere so people can look at the full completed version from the tutorial. I saw there was an example for custom_node and main_screen in the Godot demo projects, but I don't know if these tutorials would be big enough to warrant being added as a demo.

[rossunger]

I would like to there to be some examples of other types of plugins. I was struggling to find information on using "forward_canvas_gui_input" and "forward_canvas_draw_over_viewport" to draw 2d gizmo style things.

I would love to draft up a simple examples for the docs.

Also , there's a GD quest tutorial that covers some of this.

[YuriSizov]

I'm planning a complete rewrite of the section, including more explanations about related features and tutorials that cover all sorts of plugins. But if you have some suggestions about what could be a good example for some of them, feel free to describe them here!

[rossunger]

Sounds awesome! can't wait. let me know if I can help.

[Hpmason]

That'd be great! I still haven't don't much with the plugins, so it'd be great to have someone with more experience work on the examples!