Move git related things into specialized git crate

Co-Authored-By: Mikayla Maki <mikayla@zed.dev>

crates/git/src/git.rs

@@ -0,0 +1,12 @@
+use std::ffi::OsStr;
+
+pub use git2 as libgit;
+pub use lazy_static::lazy_static;
+
+pub mod diff;
+pub mod repository;
+
+lazy_static! {
+    pub static ref DOT_GIT: &'static OsStr = OsStr::new(".git");
+    pub static ref GITIGNORE: &'static OsStr = OsStr::new(".gitignore");
+}