diffs: AST based syntax diffing

[versecafe]

Closes #9721

Release Notes:

• Added syntax based diffing for git & agent diffs

Built in language git diff

Built in language agent diff

Extension based language diff

[maxbrunsfeld]

Hey @versecafe , thanks for the PR! A couple of initial questions -

1. Would it be possible to re-use imara_diff instead of wu_diff for sequence diffing that that you're doing here? It would be nice to not introduce another diffing library into the application when we already have one.
2. Can we avoid re-parsing the file on every diff? That's very inefficient, since we already maintain a parse tree of the buffer and the diff base for syntax highlighting purposes
3. What is the Syntax type? It seems like a whole other representation of a syntax tree in addition to the tree-sitter one. Is the entire tree converted into a Syntax before diffing? That seems expensive.