Theme items that don't exist in the default theme are not listed in the editor

[KoBeWi]

Godot version

4.2 251fb83

System information

Windows 10.0.19045 - Vulkan (Forward+) - dedicated NVIDIA GeForce GTX 1060 (NVIDIA; 30.0.15.1403) - Intel(R) Core(TM) i7-7700HQ CPU @ 2.80GHz (8 Threads)

Issue description

Button has icon theme item:

But it does not appear in the overrides:

Nor in the theme editor:

Steps to reproduce

1. Add Button
2. Try to find icon theme property (not the Button's own property)
3. It exists only in theory (documentation)

Minimal reproduction project

N/A

[YuriSizov]

By the way, there is also get_argument_options which uses the default theme right now, which should also be fixed to address this issue.