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/integration/tests/bisect/basic.go

@@ -7,7 +7,7 @@ import (
 
 var Basic = NewIntegrationTest(NewIntegrationTestArgs{
 	Description:  "Start a git bisect to find a bad commit",
-	ExtraCmdArgs: "",
+	ExtraCmdArgs: []string{},
 	Skip:         false,
 	SetupRepo: func(shell *Shell) {
 		shell.

pkg/integration/tests/bisect/from_other_branch.go

@@ -7,7 +7,7 @@ import (
 
 var FromOtherBranch = NewIntegrationTest(NewIntegrationTestArgs{
 	Description:  "Opening lazygit when bisect has been started from another branch. There's an issue where we don't reselect the current branch if we mark the current branch as bad so this test side-steps that problem",
-	ExtraCmdArgs: "",
+	ExtraCmdArgs: []string{},
 	Skip:         false,
 	SetupRepo: func(shell *Shell) {
 		shell.
@@ -15,7 +15,7 @@ var FromOtherBranch = NewIntegrationTest(NewIntegrationTestArgs{
 			NewBranch("other").
 			CreateNCommits(10).
 			Checkout("master").
-			RunCommand("git bisect start other~2 other~5")
+			StartBisect("other~2", "other~5")
 	},
 	SetupConfig: func(cfg *config.AppConfig) {},
 	Run: func(t *TestDriver, keys config.KeybindingConfig) {