lib/git: Fix problems caused by uses of Zsh features

[akinomyoga]

This also includes refactoring.

• 779d5fa The main fix for the uses of Zsh constructs.
• e2a9fae This is to avoid a conflict with the same name of a function defined in another file.
• 960ac25 This makes the invocation of command git for prompts and completions indirect through the function _omb_prompt_git. This will be a base for global: Specify -c core.fsmonitor= to git commands #428 and lib/omb-prompt-base: Set a timeout on git commands #173. As far as we directly call command git, we need to specify the command modifications for timeouts and git settings for every invocation of command git, which is not useful.
• ad07989 A utility function to split a string safely.
• a4e0ca1 and 4d541cf Style changes.

[akinomyoga]

@hyperupcall Hi, how are you doing? The GitHub Action lint (Check EditorConfig Format), which you introduced in #433, has been very helpful so far. Thank you! I'm reaching out to you because a few days ago, the action seems to have started to always produce an error. Could you take the time to look at it when you have time? It seems to be related to the Go version of the environment, but I haven't carefully examined it.

[hyperupcall]

Hey! I'll take a look at it tomorrow. My best guess right now is that an invalid assumption about modules was made, like in relation to GO111MODULEs.

Edit: Here is the root cause: editorconfig/editorconfig-core-go@73c37c4

[akinomyoga]

Thank you!