This patch adds a new CLI parameter to the `create-window` subcommand,
matching the existing `--option` parameter when creating a new Alacritty
instance.

This parameter allows setting up the initial window configuration from
the CLI without having to call `alacritty msg config`, making sure that
all options are set appropriately right from the start.

Closes #6238.

This patch applies all breaking and non-breaking dependency updates
and bumps MSRV to 1.70.0.

This switches Alacritty's default configuration format from yaml to
toml. While yaml is still supported, it is done by converting it to toml
and should be removed entirely in the future.

All existing features were persisted based on my testing. Behavior
should not change much, though `--option` might have slightly different
behavior since the entire line is not interpreted as one line of toml.

A new `alacritty migrate` subcommand has been added which allows
automatic migration from yaml to toml. This also could be used as a
facility to automatically fix configuration file changes in the future.

Closes #6592.

Fixes #6879.
Fixes #6874.

Debian-based distributions provide a standard interface to launch a
terminal via the x-terminal-emulator name.  In order for a terminal
emualtor to satisfy that interface, it must

* Be VT100 compatiable
* Support the "-e <command> <args>" CLI option
* Support the "-T <title>" CLI option

Adjust the short form of --title accordingly, providing -t as an alias
to avoid breaking any existing usage.

This patch adds a new mechanism for changing configuration options
without editing the configuration file, by sending options to running
instances through `alacritty msg`.

Each window will load Alacritty's configuration file by default and then
accept IPC messages for config updates using the `alacritty msg config`
subcommand. By default all windows will be updated, individual windows
can be addressed using `alacritty msg config --window-id
"$ALACRITTY_WINDOW_ID"`.

Each option will replace the config's current value and cannot be reset
until Alacritty is restarted or the option is overwritten with a new
value.

Configuration options are passed in the format `field.subfield=value`,
where `value` is interpreted as yaml.

Closes #472.

This ensures that the generated completions properly suggest file paths
for arguments which accept them.

This adds the ability to pass title and class over IPC via the
create-window subcommand, so users can run only one instance for windows
of different spurposes in the window managers of their choice.

Alacritty's `msg create-window` subcommand would previously inherit all
the CLI parameters from the original executable. However not only could
this lead to unexpected behavior, it also prevents multi-window users
from making use of parameters like `-e`, `--working-directory`, or
`--hold`.

This is solved by adding a JSON-based message format to the IPC socket
messages which instructs the Alacritty server on which CLI parameters
should be used to create the new window.

Fixes #5562.
Fixes #5561.
Fixes #5560.