Is your feature request related to a problem? Please describe.
Editor-specific implementation like #4785 aside, users may have specific expectations of how their favorite editor is invoked. Their needs can never be fulfilled by adding explicit support for editors.

Taking Emacs as an example,

• A user with a lightweight Emacs configuration will likely prefer invocation as emacs --no-splash or runemacs.exe --no-splash (Windows).
• An advanced Emacs user with a heavy configuration, causing the startup process to take a significant amount of time, will likely prefer some invocation of emacsclient, but depending on operating system and preferences the details may vary, e.g.
  • emacsclient -a emacs <dirname> to handle cases when no emacs session is running a server yet.
  • emacsclient -a "emacs -Q" <dirname> if the user prefers quick startup over complete startup, if no emacs server is running yet.
  • <some wrapper script> <dirname> if the user has a more complicated setup.

Describe the solution you'd like
Adding custom command strings as External Editor option. In the command string, a pattern like %d should be replaced by the full directory path of the repository.

Describe alternatives you've considered
None really. Switching editors is not viable, and only a customizable command can fit my usage.

Teachability, Documentation, Adoption, Migration Strategy