EditorExportPlugin._supports_platform() - documentation doesn't explain how it's used

**Your Godot version:**
4.4

**Issue description:**
I'm making an addon with an export plugin that is only relevant on one platform. I saw there's a `_supports_platform` function on `EditorExportPlugin`, but I can't find any examples of how that function is used - I kinda expected if that function returns false then the export plugin would be disabled and no other functions called on it, but that doesn't seem to be the case. Searching the godot source code, I couldn't see anywhere that function is actually called from.

I suggest adding documentation for this function to explain when it's used and when you should override it.

**URL to the documentation page (if already existing):**
https://docs.godotengine.org/en/stable/classes/class_editorexportplugin.html#class-editorexportplugin-private-method-supports-platform