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/stash/apply.go

@@ -7,7 +7,7 @@ import (
 
 var Apply = NewIntegrationTest(NewIntegrationTestArgs{
 	Description:  "Apply a stash entry",
-	ExtraCmdArgs: "",
+	ExtraCmdArgs: []string{},
 	Skip:         false,
 	SetupConfig:  func(config *config.AppConfig) {},
 	SetupRepo: func(shell *Shell) {

pkg/integration/tests/stash/apply_patch.go

@@ -7,7 +7,7 @@ import (
 
 var ApplyPatch = NewIntegrationTest(NewIntegrationTestArgs{
 	Description:  "Restore part of a stash entry via applying a custom patch",
-	ExtraCmdArgs: "",
+	ExtraCmdArgs: []string{},
 	Skip:         false,
 	SetupConfig:  func(config *config.AppConfig) {},
 	SetupRepo: func(shell *Shell) {

pkg/integration/tests/stash/create_branch.go

@@ -7,7 +7,7 @@ import (
 
 var CreateBranch = NewIntegrationTest(NewIntegrationTestArgs{
 	Description:  "Create a branch from a stash entry",
-	ExtraCmdArgs: "",
+	ExtraCmdArgs: []string{},
 	Skip:         false,
 	SetupConfig:  func(config *config.AppConfig) {},
 	SetupRepo: func(shell *Shell) {

pkg/integration/tests/stash/drop.go

@@ -7,7 +7,7 @@ import (
 
 var Drop = NewIntegrationTest(NewIntegrationTestArgs{
 	Description:  "Drop a stash entry",
-	ExtraCmdArgs: "",
+	ExtraCmdArgs: []string{},
 	Skip:         false,
 	SetupConfig:  func(config *config.AppConfig) {},
 	SetupRepo: func(shell *Shell) {

pkg/integration/tests/stash/pop.go

@@ -7,7 +7,7 @@ import (
 
 var Pop = NewIntegrationTest(NewIntegrationTestArgs{
 	Description:  "Pop a stash entry",
-	ExtraCmdArgs: "",
+	ExtraCmdArgs: []string{},
 	Skip:         false,
 	SetupConfig:  func(config *config.AppConfig) {},
 	SetupRepo: func(shell *Shell) {

pkg/integration/tests/stash/rename.go

@@ -7,7 +7,7 @@ import (
 
 var Rename = NewIntegrationTest(NewIntegrationTestArgs{
 	Description:  "Try to rename the stash.",
-	ExtraCmdArgs: "",
+	ExtraCmdArgs: []string{},
 	Skip:         false,
 	SetupConfig:  func(config *config.AppConfig) {},
 	SetupRepo: func(shell *Shell) {

pkg/integration/tests/stash/stash.go

@@ -7,7 +7,7 @@ import (
 
 var Stash = NewIntegrationTest(NewIntegrationTestArgs{
 	Description:  "Stashing files directly (not going through the stash menu)",
-	ExtraCmdArgs: "",
+	ExtraCmdArgs: []string{},
 	Skip:         false,
 	SetupConfig:  func(config *config.AppConfig) {},
 	SetupRepo: func(shell *Shell) {

pkg/integration/tests/stash/stash_all.go

@@ -7,7 +7,7 @@ import (
 
 var StashAll = NewIntegrationTest(NewIntegrationTestArgs{
 	Description:  "Stashing all changes (via the menu)",
-	ExtraCmdArgs: "",
+	ExtraCmdArgs: []string{},
 	Skip:         false,
 	SetupConfig:  func(config *config.AppConfig) {},
 	SetupRepo: func(shell *Shell) {

pkg/integration/tests/stash/stash_and_keep_index.go

@@ -7,7 +7,7 @@ import (
 
 var StashAndKeepIndex = NewIntegrationTest(NewIntegrationTestArgs{
 	Description:  "Stash staged changes",
-	ExtraCmdArgs: "",
+	ExtraCmdArgs: []string{},
 	Skip:         false,
 	SetupConfig:  func(config *config.AppConfig) {},
 	SetupRepo: func(shell *Shell) {

pkg/integration/tests/stash/stash_including_untracked_files.go

@@ -7,7 +7,7 @@ import (
 
 var StashIncludingUntrackedFiles = NewIntegrationTest(NewIntegrationTestArgs{
 	Description:  "Stashing all files including untracked ones",
-	ExtraCmdArgs: "",
+	ExtraCmdArgs: []string{},
 	Skip:         false,
 	SetupConfig:  func(config *config.AppConfig) {},
 	SetupRepo: func(shell *Shell) {

pkg/integration/tests/stash/stash_staged.go

@@ -7,7 +7,7 @@ import (
 
 var StashStaged = NewIntegrationTest(NewIntegrationTestArgs{
 	Description:  "Stash staged changes",
-	ExtraCmdArgs: "",
+	ExtraCmdArgs: []string{},
 	Skip:         false,
 	SetupConfig:  func(config *config.AppConfig) {},
 	SetupRepo: func(shell *Shell) {

pkg/integration/tests/stash/stash_unstaged.go

@@ -7,7 +7,7 @@ import (
 
 var StashUnstaged = NewIntegrationTest(NewIntegrationTestArgs{
 	Description:  "Stash unstaged changes",
-	ExtraCmdArgs: "",
+	ExtraCmdArgs: []string{},
 	Skip:         false,
 	SetupConfig:  func(config *config.AppConfig) {},
 	SetupRepo: func(shell *Shell) {