Retain commit message when cycling history

When cycling history, we want to make it so that upon returning to the original prompt, you get your text back.
Importantly, we don't want to use the existing preservedMessage field for that because that's only for preserving
a NEW commit message, and we don't want the history stuff of the commit reword flow to overwrite that.

pkg/integration/tests/commit/history.go

@@ -0,0 +1,53 @@
+package commit
+
+import (
+	"github.com/jesseduffield/lazygit/pkg/config"
+	. "github.com/jesseduffield/lazygit/pkg/integration/components"
+)
+
+var History = NewIntegrationTest(NewIntegrationTestArgs{
+	Description:  "Cycling through commit message history in the commit message panel",
+	ExtraCmdArgs: "",
+	Skip:         false,
+	SetupConfig:  func(config *config.AppConfig) {},
+	SetupRepo: func(shell *Shell) {
+		shell.EmptyCommit("initial commit")
+		shell.EmptyCommit("commit 2")
+		shell.EmptyCommit("commit 3")
+
+		shell.CreateFile("myfile", "myfile content")
+	},
+	Run: func(t *TestDriver, keys config.KeybindingConfig) {
+		t.Views().Files().
+			IsFocused().
+			PressPrimaryAction(). // stage file
+			Press(keys.Files.CommitChanges)
+
+		t.ExpectPopup().CommitMessagePanel().
+			InitialText(Equals("")).
+			Type("my commit message").
+			SelectPreviousMessage().
+			Content(Equals("commit 3")).
+			SelectPreviousMessage().
+			Content(Equals("commit 2")).
+			SelectPreviousMessage().
+			Content(Equals("initial commit")).
+			SelectPreviousMessage().
+			Content(Equals("initial commit")). // we hit the end
+			SelectNextMessage().
+			Content(Equals("commit 2")).
+			SelectNextMessage().
+			Content(Equals("commit 3")).
+			SelectNextMessage().
+			Content(Equals("my commit message")).
+			SelectNextMessage().
+			Content(Equals("my commit message")). // we hit the beginning
+			Type(" with extra added").
+			Confirm()
+
+		t.Views().Commits().
+			TopLines(
+				Contains("my commit message with extra added").IsSelected(),
+			)
+	},
+})