Fixes #5256

This updates the macOS apprt to implement the `OPEN_URL` apprt action to
use the NSWorkspace APIs instead of the `open` command line utility.

As part of this, we removed the `ghostty_config_open` libghostty API and
instead introduced a new `ghostty_config_open_path` API that returns the
path to open, and then we use the `NSWorkspace` APIs to open it (same
function as the `OPEN_URL` action).

It was unused and doesn't match our diagnostic API.

Rather than storing a list of errors we now store a list of
"diagnostics." Each diagnostic has a richer set of structured
information, including a message, a key, the location where it occurred.

This lets us show more detailed messages, more human friendly messages, and
also let's us filter by key or location. We don't take advantage of
all of this capability in this initial commit, but we do use every field
for something.

Fixes #1802 

This allows `keybind` configurations to map to any Unicode codepoint. This enables keybindings for which we don't have a registered keycode or for custom keyboard firmwares that may produce arbitrary text (but the Ghostty support is limited to a single codepoint).

The `keybind` syntax is unchanged. If a bound character doesn't map to a known logical key that Ghostty knows about, we map it to a Unicode codepoint. The unicode codepoint is compared against the _unshifted codepoint_ from the apprt key event. 

Note that this binding is to a single _codepoint_. We don't support arbitrary sequences of characters or multi-code point graphemes for keybindings due to the complexity in memory management that would introduce.

This also provides a good fallback for scenarios where it might make sense to educate Ghostty about a key code or fix a bug in our keyboard input system, but the unicode data is correct. In that scenario, unicode key binds should allow key binds to still work while we investigate the input issues.

Example:

```
shift+ö=text:hello
```

This now works as expected on a US hardware keyboard with the Hungarian keyboard layout.

- Settings shortcut opens the config file in the default editor.

Signed-off-by: Borja Clemente <borja.clemente@gmail.com>