Consider current branch for open command

[David Van Loon]

When using the Bitbucket: Open command, take into account the current git branch and open the same branch in Bitbucket.

For example, if I am looking at a file in VS Code that exists on the develop branch, but not on the master branch, the Bitbucket: Open command will attempt to display the file from the default branch in Bitbucket (master in this case). The attempt will fail as the file doesn't exist in that branch. The desired action is that the extension will open Bitbucket at the specified branch (develop in this case).

In my example, rather than the following: https://bitbucket.example.com/projects/PROJ/repos/repo-name/browse/filename.json#23-23

Open the following: https://bitbucket.example.com/projects/PROJ/repos/repo-name/browse/filename.json?at=refs%2Fheads%2Fdevelop#23-23

This is using Bitbucket Server.