Add support for git mergetool

[jelmer]

Add support for the git mergetool command, which runs merge conflict resolution tools to help users resolve merge conflicts.

Description:
The git mergetool command launches an interactive merge resolution program to resolve merge conflicts. It can use various merge tools like vimdiff, meld, kdiff3, etc.

Common use cases:

• Resolving merge conflicts during git merge operations
• Using graphical tools to visualize and resolve conflicts
• Automating conflict resolution workflows in development environments

This would enhance dulwich's porcelain interface by providing a user-friendly way to handle merge conflicts.

[rs545837]

On the merge driver side (complementary to mergetool), weave is a tree-sitter-based merge driver that resolves conflicts at the entity level (functions, classes) before they even reach the mergetool stage. It plugs into git's merge driver interface and handles the common case where two branches add different functions to the same file. Might be worth considering as a reference for how merge drivers work alongside mergetools.

[jelmer]

@rs545837 Ah, interesting - is there a python interface for weave?

[rs545837]

Hey @jelmer, yeah you don't need a different python interface, its basically a merge driver, once you set it up, it will integrate in your git command line, I was actually curious to see new kind of diff and then came up with a new merge tool, and had an email exchange with creator of git merge who also got excited about this.