Hint when execute run shell command inserting

[Renkai]

When we use :sh, we can get hint like directory and file names, but when we execute !(Run shell command, inserting output before each selection), we don't have this feature, can we let it has this feature as also?

[the-mikedavis]

The shell commands open a prompt with no completion:

helix/helix-term/src/commands.rs

Lines 5197 to 5202 in d5fec30

	fn shell_prompt(cx: &mut Context, prompt: Cow<'static, str>, behavior: ShellBehavior) {
	ui::prompt(
	cx,
	prompt,
	Some('|'),
	ui::completers::none,

That could be changed to the filename completer to match :run-shell-command:

helix/helix-term/src/commands/typed.rs

Lines 2707 to 2713 in d5fec30

	TypableCommand {
	name: "run-shell-command",
	aliases: &["sh"],
	doc: "Run a shell command",
	fun: run_shell_command,
	signature: CommandSignature::all(completers::filename)
	},