This patch adds a new add_tab() function in GUI::SettingsWindow that
takes an already created NonnullRefPtr<Tab> object. This allows us to
handle errors while creating the Tab object and then pass it to this
function to actually add the object to the SettingsWindow.
We have a new, improved string type coming up in AK (OOM aware, no null
state), and while it's going to use UTF-8, the name UTF8String is a
mouthful - so let's free up the String name by renaming the existing
class.
Making the old one have an annoying name will hopefully also help with
quick adoption :^)
SettingsWindow now notices if the window is marked as modified, and
shows a confirmation pop-up to check if the user wants to apply or
discard their changes. It automatically marks the window as unmodified
after restoring defaults or applying the changes, but each Tab subclass
needs to call `set_modified(true)` when the user modifies things.
The "Apply" button is automatically disabled when there are no unsaved
changes to be applied.
In order to propagate errors that occur during UI setup, we have to move
all that logic out of widget/window subclass constructors. This is a
first attempt at doing that, for GUI::SettingsWindow.
Some settings tabs, like the ones on the upcoming terminal settings,
need to know when the cancel button is pressed to clean up things like
temporary live updates. Therefore, the SettingsWindow::Tab now features
a cancel_settings callback which does not need to be implemented.
The FooSettings apps have quite a lot of boilerplate just around
creating a tabbed window with the same styling and the same row of
buttons along the bottom. So, let's extract that out into a class we can
reuse! :^)
You create a SettingsWindow instead of a regular Window, passing a title
and a flag to determine if a "Defaults" button is shown. Then call
add_tab() to add tabs to it. Tabs are widgets extending
SettingsWindow::Tab, which has methods for saving and resetting the
values.
