List `@export_file` behavior change as a breaking change in the 4.3->4.4 upgrade page

**Your Godot version:** 4.4.stable

**Issue description:**
The change to how `@export_file` works from 4.3 to 4.4 was a breaking change!
Regardless of PR https://github.com/godotengine/godot/pull/105414 (which adds `@export_file_path` to 4.5 for those who want the old behavior), the fact `@export_file` behavior changed needs to be added as a breaking change in [Upgrading from Godot 4.3 to Godot 4.4](https://docs.godotengine.org/en/stable/tutorials/migrating/upgrading_to_godot_4.4.html). Hopefully this can be added right away to the online docs without depending on new Godot versions? (I don't know how this works)

**URL to the documentation page:**
https://docs.godotengine.org/en/stable/tutorials/migrating/upgrading_to_godot_4.4.html

See:
- https://github.com/godotengine/godot/issues/104379
- https://github.com/godotengine/godot/issues/104818
- https://github.com/godotengine/godot/pull/105414#issuecomment-2968449078
- [This comment](https://github.com/godotengine/godot-docs/pull/11029#issuecomment-2980701383)

For example:
In **Breaking changes > Core** and/or **Behavior Changes > Core**
> [!NOTE]
> Annotation `@export_file` now prefers to store and return a `uid://…` instead of a `res://…` path. When changing a value in the inspector, its format will change to uid. This can make you have mixed uid and res paths even within an array.
> Project settings will also store files as uid when you set or change a value.

Maybe also include something like:
> In 4.5 you can keep the 4.3 behavior of `@export_file` by using `@export_file_path` instead.
> In 4.4, the only way to preserve the old behavior is by manually setting the `res://…` path in `*.tscn`/`*.tres` files using a text editor whenever you need to change these fields.