config: Use env instead of code generation

Code generation messes with the actual source directory and makes it
impossible to use tools like clippy without having generated the config
via meson.

src/config.rs

@@ -0,0 +1,28 @@
+// Copyright (c) 2024 Sophie Herold
+//
+// This program is free software: you can redistribute it and/or modify
+// it under the terms of the GNU General Public License as published by
+// the Free Software Foundation, either version 3 of the License, or
+// (at your option) any later version.
+//
+// This program is distributed in the hope that it will be useful,
+// but WITHOUT ANY WARRANTY; without even the implied warranty of
+// MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+// GNU General Public License for more details.
+//
+// You should have received a copy of the GNU General Public License
+// along with this program.  If not, see <http://www.gnu.org/licenses/>.
+//
+// SPDX-License-Identifier: GPL-3.0-or-later
+
+pub const APP_ID: &str = default_env(option_env!("APP_ID"), "org.gnome.Loupe.Devel");
+pub const PROFILE: &str = default_env(option_env!("PROFILE"), ".Devel");
+pub const VERSION: &str = default_env(option_env!("VERSION"), "unknown");
+pub const LOCALEDIR: &str = default_env(option_env!("LOCALEDIR"), "/usr/share/locale/");
+
+const fn default_env(v: Option<&'static str>, default: &'static str) -> &'static str {
+    match v {
+        Some(v) => v,
+        None => default,
+    }
+}