Steps to reproduce:
1. Start TextEditor and make some changes to the document.
2. Try to open an existing file.
3. When prompted choose to save the changes to the existing document.
4. Close the file picker by clicking 'Cancel'.
5. Note how the file was opened anyway and your changes were lost.
Same applies to the 'New File' action.
Previously, AK::Function would accept _any_ callable type, and try to
call it when called, first with the given set of arguments, then with
zero arguments, and if all of those failed, it would simply not call the
function and **return a value-constructed Out type**.
This lead to many, many, many hard to debug situations when someone
forgot a `const` in their lambda argument types, and many cases of
people taking zero arguments in their lambdas to ignore them.
This commit reworks the Function interface to not include any such
surprising behaviour, if your function instance is not callable with
the declared argument set of the Function, it can simply not be
assigned to that Function instance, end of story.
This moves the calculation of selected words that was originally
in the TextEditor application to TextEditor in LibGUI.
This allows all applications with text editors to get
this number without having to calculating it themselves.
This changes (context) menus across the system to conform to titlecase
capitalization and to not underline the same character twice (for
accessing actions with Alt).
The HTML and Markdown preview modes both use an OutOfProcessWebView to
render the preview pane, and we were instantiating this view from GML.
This caused us to always spawn a WebContent process alongside every
TextEditor instance.
Fix this by deferring the OOPWV construction until we actually need it.
This makes launching TextEditor on a text file quite a bit faster. :^)
This was quite unreliable before. Changes to the undo stack's modified
state are now reflected in the document's modified state, and the
GUI::TextEditor widget has its undo/redo actions updated automatically.
UndoStack is still a bit hard to understand due to the lazy coalescing
of commands, and that's something we should improve upon (e.g with more
explicit, incremental command merging.) But for now, this is a nice
improvement and undo/redo finally behaves in a way that feels natural.
Instead of tracking this stuff ourselves at the application level,
we now just act as an intermediary and pass along the information to
the windowing system.
