Add LibreMerge

[iagodpassos]

Adds LibreMerge, a free differencing and merging tool for Linux and macOS (GPL-3.0-or-later): a Qt 6 port of the WinMerge comparison engine with side-by-side file compare and merge (2- and 3-way), folder comparison, CSV/TSV table comparison, image comparison, syntax highlighting, and light/dark themes.

AppImages for x86_64 and aarch64 are published on the GitHub releases page. The x86_64 AppImage was tested on a clean Ubuntu 22.04 (offscreen and X11/Xvfb) with the app's built-in selftests.

[github-actions]

❌ Test failure

Compatibility: not self-contained: uses the C library of the system; references glibc 2.36

• The AppImage was built on a system that is too new. Please build it on the oldest still-supported Ubuntu LTS release so that it runs on all supported systems.
• The application quit or crashed right after starting. The error below usually shows why.

First error in the log:

/run/firejail/appimage/AppRun.wrapped: /lib/x86_64-linux-gnu/libc.so.6: version `GLIBC_2.36' not found (required by /run/firejail/appimage/usr/bin/../lib/libarchive.so.13)

ERROR: The application exited within 11 seconds instead of showing a window

Commit 3b41c2b. Full log