git: add GitScmProvider.unstageAll unit tests

[Hanksha]

What it does

Closes #11801.

This PR fixes the missing reset index option when calling unstage which is required to properly unstage all the staged changes. It also adds a unit test for it.

How to test

1. Create a directory
2. Run git init in that directory
3. Create a sample test.txt file
4. Open Theia with that directory as workspace
5. Go to Source Control view
6. Use the Unstage All via the button or tab bar dropdown menu

Review checklist

• As an author, I have thoroughly tested my changes and carefully followed the review guidelines

Reminder for reviewers

• As a reviewer, I agree to behave in accordance with the review guidelines

Signed-off-by: Vivien Jovet [email protected]

[vince-fugnitto]

@Hanksha the ECA check is failing since it cannot find [email protected] registered (your personal email was used in the past).

[Hanksha]

@vince-fugnitto I fixed it, created an account and signed the ECA. I did this on behalf of Toro Cloud so I use that email to sign the commit this time.

[Hanksha]

@vince-fugnitto Can you have a look at the test again? I changed it to use the actual Git implementation and a git repo on the filesystem.

[vince-fugnitto]

The new unit test looks good to me 👍
I merged the actual unstageAll fix yesterday for yesterday's v1.31.0 release so you can rebase and squash locally first :)

[Hanksha]

@vince-fugnitto Done!

By the way, isn't #11801 missing from CHANGELOG.md for 1.31.0?

[vince-fugnitto]

LGTM 👍