Add apple_platform feature to check if running on apple platform

[OzelotVanilla]

What it can do ?

This helps to determine at least about whether the CTRL or the META should be used for shortcut.

Motivation

Reduce manually checking like this.

godot/core/os/keyboard.cpp

Line 373 in efb40c1

if (OS::get_singleton()->has_feature("macos") || OS::get_singleton()->has_feature("web_macos") || OS::get_singleton()->has_feature("web_ios")) {

Mentioned also in the comment of #108034 (comment), which is about the checking logic of whether current platform is apple or not.

TODO

If it is necessary to do so, I will add also the doc and core-bind.

[OzelotVanilla]

Seems like has_feature is not const (should it be ?).

So this is_apple_platform is also leaved non-const currently.

[AdriaandeJongh]

why not just add a feature tag to all platforms using the apple platform, using the feature system that was already built precisely for this?

[OzelotVanilla]

why not just add a feature tag to all platforms using the apple platform, using the feature system that was already built precisely for this?

Thank you! Let me change it later.

[adamscott]

I'm against the premise of the PR. We should have instead an OS method that explicitly says if Ctrl or Meta should be used. I'm writing a proposal right now.

[OzelotVanilla]

I'm against the premise of the PR. We should have instead an OS method that explicitly says if Ctrl or Meta should be used. I'm writing a proposal right now.

The motivation (I would not think it as a premise) here is truly get the corresponding CTRL key, but since I do not know what is the other usage of doing checking feature apple_platform could help, so I could not say if this feature is really helpful in other situation or not.