Refactor: Replace deferred code in edit commands with functions

[sandr01d]

Check list

• [X] I have performed a self-review of my code
• [ ] I have commented my code in hard-to-understand areas
• [ ] I have made corresponding changes to the documentation

Description

_forgit_diff and _forgit_add allow editing the currently previewed file in the EDITOR. This used to be handled entirely using deferred code. This PR replaces the deferred code and binds the commands to functions instead.

Note

This PR belongs to #326 and resulted from discussions in #324.

Type of change

• [ ] Bug fix
• [ ] New feature
• [X] Refactor
• [ ] Breaking change
• [ ] Documentation change

Test environment

• Shell
  • [ ] bash
  • [X] zsh
  • [ ] fish
• OS
  • [X] Linux
  • [ ] Mac OS X
  • [ ] Windows
  • [ ] Others:

[sandr01d]

@carlfriedrich Scratch my earlier comment about doing _forgit_extract_sha first. Looking into this I figured that doint the execute-silent commands first will add less friction.

[sandr01d]

Good finds @carlfriedrich, thanks! I've implemented as requested. Rerequesting your review.

[sandr01d]

Changes have been merged with #326