Version height computed to be 0 when project is built with path with non-canonical casing

[AArnott]

When a project's repo-relative path is reported as a/b but git records it as A/b, we fail to walk the tree in searching for version.json files. If the version.json file appears under that path, we can end up with a version height of 0:

The failing line is:

Nerdbank.GitVersioning/src/NerdBank.GitVersioning/Managed/ManagedVersionFile.cs

Line 170 in bf2ade8

tree = this.Context.Repository.GetTreeEntry(tree, GitRepository.Encoding.GetBytes(directoryName));

We should probably have a fallback path here where we allow for case-insensitive matches when the git settings for the repo indicate case insensitivity is preferred.

We should add an automated test that runs against both managed and libgit2 implementations.