Add RevWalker

[jairbubbles]

• Add class wrapper other https://github.com/libgit2/libgit2/blob/main/include/git2/revwalk.h to allow reusing it for multiple traversals
• Expose git_revwalk_push_glob / git_revwalk_hide_glob and git_revwalk_push_ref / git_revwalk_hide_ref which allows to select commits more efficiently
• Use the wrapper in the CommitLog

This allows more flexibility than CommitLog and allows to traverse the repository multiple times more efficiently.

usingvarrepository=newRepository(@"<repo_path>");usingvarrevWalker=newRevWalker(repository);// Store commits in a cache to speed up multiple walks on same repositoryvarcommitsCache=newDictionary<ObjectId,Commit>();revWalker.Reset();revWalker.Sorting(CommitSortStrategies.Topological);revWalker.PushGlob("refs/tags/*");varcommits=GetCommits().ToArray();// Subsequent walk will reuse commits cache and internal RevWalker cacherevWalker.Reset();revWalker.PushRef("HEAD");commits=GetCommits().ToArray();IEnumerable<Commit>GetCommits(){while(true){varobjectId=revWalker.Next();if(objectId==null)break;if(!commitsCache.TryGetValue(objectId,outvarcommit)){commit=repository.Lookup<Commit>(objectId);commitsCache[objectId]=commit;}yieldreturncommit;}}