Add key binding for switching from the commit message panel to an editor

This is useful for when you begin to type the message in lazygit's commit panel,
and then realize that you'd rather use your editor's more powerful editing
capabilities. Pressing <c-o> will take you right there.

pkg/gui/context/commit_message_context.go

@@ -32,6 +32,8 @@ type CommitMessageViewModel struct {
 	preservedMessage string
 	// invoked when pressing enter in the commit message panel
 	onConfirm func(string, string) error
+	// invoked when pressing the switch-to-editor key binding
+	onSwitchToEditor func(string) error
 
 	// The message typed in before cycling through history
 	// We store this separately to 'preservedMessage' because 'preservedMessage'
@@ -98,10 +100,12 @@ func (self *CommitMessageContext) SetPanelState(
 	descriptionTitle string,
 	preserveMessage bool,
 	onConfirm func(string, string) error,
+	onSwitchToEditor func(string) error,
 ) {
 	self.viewModel.selectedindex = index
 	self.viewModel.preserveMessage = preserveMessage
 	self.viewModel.onConfirm = onConfirm
+	self.viewModel.onSwitchToEditor = onSwitchToEditor
 	self.GetView().Title = summaryTitle
 	self.c.Views().CommitDescription.Title = descriptionTitle
 }
@@ -117,3 +121,11 @@ func (self *CommitMessageContext) RenderCommitLength() {
 func getBufferLength(view *gocui.View) string {
 	return " " + strconv.Itoa(strings.Count(view.TextArea.GetContent(), "")-1) + " "
 }
+
+func (self *CommitMessageContext) SwitchToEditor(message string) error {
+	return self.viewModel.onSwitchToEditor(message)
+}
+
+func (self *CommitMessageContext) CanSwitchToEditor() bool {
+	return self.viewModel.onSwitchToEditor != nil
+}