Make branch name comparison case insensitive

[asbjornu]

Description

This PR introduces the IsEquivalentTo() extension method to System.String and uses it to make branch name comparison case insensitive.

Related Issue

Fixes #864.

Motivation and Context

Working on Windows with a case insensitive file system and running GitVersion in a CI/CD pipeline on Linux, the case sensitivity of Linux often cause problems that aren't discovered on Windows. This change should remedy that discrepancy.

How Has This Been Tested?

I added a poorly constructed test to provoke the issue. Not optimal, but better than nothing. 🤷‍♂️

Checklist:

• My code follows the code style of this project.
• My change requires a change to the documentation.
• I have updated the documentation accordingly.
• I have added tests to cover my changes.
• All new and existing tests passed.

[asbjornu]

I'm not happy how the test turned out, but it's better than nothing I guess.

[arturcic]

I like the way you abstracted the Commands and included as part of GitRepository.

In version 6.0 I would want to move the LibGit2Sharp code into a separate class, maybe we can move it outside of the Core. And if have luck we might have 2 implementations, one with LibGit2Sharp and other with let's say Octokit

[asbjornu]

Yes, that would be ideal, @arturcic! A dependency-free Core would be awesome.

[arturcic]

As part of part di4 I tried to move the libgit2sharp code to IRepositoryMetadataProvider and RepositoryExtensions and added as injectable IRepository, now in the next iteration we need to create our version of IRepository interface, Branch, Commit classes, and then we can reduce the dependency of the code on Libgit2Sharp

[arturcic]

When the build succeeds feel free to merge it yourself. Just add the milestone to the issue you're fixing so it is included in the release notes

[mcascone]

Please see my comment on the original issue: I am seeing this problem in 5.10.3 right now.

[asbjornu]

The error you're seeing is not related to this, @mcascone, as GitVersion is not throwing the error message you're seeing. It is libgit2 trying to create the branch develop when Develop already exists, which is a filesystem case sensitivity issue that can only be resolved by you using all-lowercase branch names consistently.