before: gitrepo vs git packages
after: git package fully handle all git operations
by the way, use `WithRepo(repo)` instead of `WithDir(repo.Path)` to hide
path details.
benefits:
1. remove all unnecessary wrappers, developers no need to struggle with
"which package should be used"
2. simplify code, RepositoryFacade can (will) be used everywhere, all
"path" details are (will be) hidden
1. Storing "ctx" in a long-living object is wrong
2. Make the commit & tree cacheable (for the future performance
optimization)
3. Also fix some bad designs like `// FIXME: bad design, this field can
be nil if the commit is from "last commit cache"`
ref:
* #33893
Most time, when invoking `git.OpenRepository`, `objectFormat` will not
be used, so it's a waste to invoke commandline to get the object format.
This PR make it a lazy operation, only invoke that when necessary.
