Add option to allow echo events in menu shortcuts

[KoBeWi]

I implemented this for #28427, but then realized I can close that issue without adding new functionality.

Luckily I kept the code, because apparently this is useful for #31739
To use this in editor, you need to add false, true to editor shortcut, e.g.

edit_menu->get_popup()->add_shortcut(ED_GET_SHORTCUT("script_text_editor/delete_line"), EDIT_DELETE_LINE, false, true);

EDIT:
Well, the issue is now closed, but there is still #28607

EDIT2:
Fixes #79181

Supersedes #64317
Supersedes #79564

[KoBeWi]

Rebased (21k commits behind, I think it's the highest count I ever had in a PR xd)

I also added echo usage to EditorNode's undo/redo commands, so that the new functionality is not unused.

Note that there is #64317, which does the same thing, but might be more complete.

[akien-mga]

Wouldn't this be way too sensitive? Or is there a feature already so that multiple India would only be triggered when holding the keys long enough?

[KoBeWi]

This just allows to trigger shortcuts continuously (echo events have some delay, so it's not spammed each frame or anything). We have some shortcuts that could benefit from this, because right now they do manual checks in _unhandled_key_input() to enable continuous use.

[Calinou]

This is definitely something I'd like to see for some shortcuts, such as undo/redo. In most other apps, you can hold Ctrl + Z or Ctrl + Y to continuously undo/redo a lot of steps. I'm not sure if this behavior should be made the default though.

[KoBeWi]

Updated the PR with some more code.
Seems like it fixes a usability issue and keeps getting duplicates, so we should try merging this soon 🙃

[akien-mga]

Looks good to me, but you need to add compat methods since adding a new argument (even with a default value) breaks compat for GDExtension.

See e.g. TileMap::get_used_rect for an example on how to do this.

[akien-mga]

Ah you also need to acknowledge the change with:

diff --git a/misc/extension_api_validation/4.0-stable.expected b/misc/extension_api_validation/4.0-stable.expected
index 823af03c8e..5f982cbff6 100644
--- a/misc/extension_api_validation/4.0-stable.expected
+++ b/misc/extension_api_validation/4.0-stable.expected
@@ -443,3 +443,11 @@ Validate extension JSON: API was removed: classes/SystemFont/properties/fallback
 
 The property was moved to their common base class Font.
 The setters and getters were already in Font, so this shouldn't affect compatibility.
+
+
+GH-36493
+--------
+Validate extension JSON: Error: Field 'classes/PopupMenu/methods/add_icon_shortcut/arguments': size changed value in new API, from 4 to 5.
+Validate extension JSON: Error: Field 'classes/PopupMenu/methods/add_shortcut/arguments': size changed value in new API, from 3 to 4.
+
+Added optional argument. Compatibility methods registered.

[akien-mga]

Should finally pass CI this time :)

[akien-mga]

Thanks!