fix: #200773, handle branch creation in new repos

[kunalpanchal]

Fixes #200773

• improve target handling in branch command
• handle branch creation in new repos

Steps to test:

• Create new folder and enter folder: mkdir test1 && cd test1
• Open vscode: `code . --disable-extensions
• Use activity bar to initialize new repo
• Create new text file but don't check it in
• Use command palette to create new branch Git: Create Branch with name test
• No more error - "Error: Git: fatal: Head is not a commit and a branch test cannot be created from it"

[kunalpanchal]

@microsoft-github-policy-service agree