Project Manager: Open project when "Enter" is pressed when the search box is focused

[alfredbaudisch]

In the project manager, when the Search Box is focused, the Key::Enter event is not being handled by ProjectManager::shortcut_input. So added a dedicated handler for the search box with the signal gui_input. Now when Enter is pressed, the highlighted project is opened.

Fixes and closes #73768.

[akien-mga]

Makes sense. But LineEdit has a text_submitted signal exactly for this, you don't need to reimplement it via _gui_input.

[alfredbaudisch]

Makes sense. But LineEdit has a text_submitted signal exactly for this, you don't need to reimplement it via _gui_input.

Done 👍

[akien-mga]

Thanks!