feat(fish): use abbr instead of alias

[folliehiyuki]

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

• Switch from aliases to abbreviations, as I suggested in https://github.com/wfxr/forgit/pull/344#issuecomment-1930072329
• string collect returns 1 on empty argument, so it's used here to avoid repeating if else end blocks. Another benefit is that the output of string collect is ensured to be a single string. From string --help:

  string collect collects its input into a single output argument, without splitting the output when used in a command substitution. This is useful when trying to collect multiline output from another command into a variable. Exit status: 0 if any output argument is non-empty, or 1 otherwise.

This PR is marked as breaking change, since abbr behaves differently from alias. It can only be used in the interactive command line (so putting exec glo into your scripts won't work).

Type of change

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

Test environment

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