VTE maintains a two-layer color system where colors set via OSC 10/11
escape sequences take precedence over colors set via the API When
switching profiles, the API-layer colors were updated but any active OSC
overrides would persist, causing the profile's colors to be ignored.
This feeds OSC 110/111 reset sequences after setting profile colors to
clear the override layer.

Use the current directory URI (set by the shell via OSC 7 escape
sequence) to determine the working directory for new tabs, instead of
reading /proc. This works inside tmux/screen/sudo, preserves symlink
components, and is consistent with other VTE-based terminal emulators.

The /proc-based detection is kept as a fallback for shells that don't
emit OSC 7 (e.g. vte.sh is not sourced). The initial working directory
is used as a final fallback, and the separate _with_fallback variant is
folded into the main function so all callers benefit from the complete
fallback chain.

Adapted from https://gitlab.gnome.org/GNOME/gnome-terminal/-/commit/cf3cad87

Fixes #195

The built-in color scheme dropdown always showed "Custom" when reopening
the profile editor. Two bugs were present:

- color comparison was called as pointer-to-pointer comparison, which
  always fails.

- gdk_rgba_equal does exact floating-point comparison, which is too
  strict for colors that have been round-tripped through GSettings
  string serialization. Using the fuzzy rgba_equal function fixes that.

Fixes #486

When curses programs send empty title escape sequences on exit, the
window title would become blank in replace mode instead of reverting to
the initial title. Fix by checking for both NULL and empty string before
falling back to the static title.

Fixes #479

Store and persist window icons in session config files. Icons set via
the command line are now saved during session management and restored
when loading config files.

Also adds error reporting for invalid icon file paths.

Since profiles do not provide a way of setting the window icon, we
re-introduce the --icon option to allow the window instance to report an
icon programmatically.

Fixes https://github.com/mate-desktop/mate-terminal/issues/246

It seems Wayland-based window managers provide additional decorations
that we're not tracking in our "preferred size" computations. This means
every geometry update shrinks the window by a bit.

Factor in the allocated dimensions, not just the preferred ones.

Borrows some ideas from
https://bugzilla.gnome.org/show_bug.cgi?id=769898

I also drop a few unused values leftover from gnome-terminal.

Fixes #350

The `uris_as_paths` member, which is set to `true` when the paste
command has been triggered by the **Paste Filenames** action, was being
checked too late: a file URI was ultimately being entered to the
terminal, as opposed to the expected plain text version.

Test plan:

- Copy a file in Caja, or in any other file explorer that inserts the
  `text/uri-list` and `text/plain` MIME formats into the clipboard.
- Paste the file in a MATE Terminal either via `Ctrl+Shift+V`, or via
  the **Paste** action in the context menu.

Without this change, a file URI is entered. For example:

```
file:///home/jane.doe/my%20pictures/foo%20bar.jpg
```

With this change, a regular filepath [that the filesystem can recognize]
is pasted. For example:

```
/home/jane.doe/my pictures/foo bar.jpg
```

Note that the behavior of the **Paste Filenames** context menu action
remains unchanged (i.e. file URIs are still converted to regular paths
surrounded by single quotes).

Do not show the tab rename dialog when terminal window content is doubleclicked in terminal apps using the mouse