Construct arg vector manually rather than parse string

By constructing an arg vector manually, we no longer need to quote arguments

Mandate that args must be passed when building a command

Now you need to provide an args array when building a command.
There are a handful of places where we need to deal with a string,
such as with user-defined custom commands, and for those we now require
that at the callsite they use str.ToArgv to do that. I don't want
to provide a method out of the box for it because I want to discourage its
use.

For some reason we were invoking a command through a shell when amending a
commit, and I don't believe we needed to do that as there was nothing user-
supplied about the command. So I've switched to using a regular command out-
side the shell there

pkg/gui/controllers/helpers/mode_helper.go

@@ -2,6 +2,7 @@ package helpers
 
 import (
 	"fmt"
+	"strings"
 
 	"github.com/jesseduffield/generics/slices"
 	"github.com/jesseduffield/lazygit/pkg/commands/types/enums"
@@ -53,7 +54,7 @@ func (self *ModeHelper) Statuses() []ModeStatus {
 					fmt.Sprintf(
 						"%s %s",
 						self.c.Tr.LcShowingGitDiff,
-						"git diff "+self.diffHelper.DiffStr(),
+						"git diff "+strings.Join(self.diffHelper.DiffArgs(), " "),
 					),
 					style.FgMagenta,
 				)