Fixes#1724
See background in #1724. The general idea is that for Ghostty
invocations via xdg-terminal-exec, we set the initial title to the
command automatically so that window managers can modify the styling.
We only do this for xdg-terminal-exec because that protocol/spec is
specifically for the scenario that the terminal is being used to launch
a command from the desktop environment.
For now, bash integration must be explicitly enabled (by setting
`shell-integration = bash`). Our automatic shell integration requires
bash version 4 or later, and systems like macOS continue to ship bash
version 3 by default. This approach avoids the cost of performing a
runtime version check.
Related to #1802
CSIu format sends a unicode codepoint but we were just sending the first
byte of the utf8 sequence, which is very much not right. This fixes that
by parsing the utf-8.
It isn't defined what to do if the utf-8 sequence is invalid or has
multiple codepoints so we just skip CSIu encoding in that case.
Reproduction: HU layout Ctrl+ő
On release, we were previously not sending an alt text (we were sending
it properly on press). Kitty sends it also on release and the spec makes
it clear we should send it on release. This was just due to some faulty
logic; added a test and fixed that.
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.
