chore(exec): small API edits (#323)

* feat: add OSExec helper function for running exec.Cmds

* chore: for now, un-expose WrapExecCommand

* chore: move exec struff into its own file

* chore(exec): better name for Exec func that wraps exec.Cmd (thanks, @toby)

examples/exec/main.go

@@ -12,7 +12,7 @@ type editorFinishedMsg struct{ err error }
 
 func openEditor() tea.Cmd {
 	c := exec.Command(os.Getenv("EDITOR")) //nolint:gosec
-	return tea.Exec(tea.WrapExecCommand(c), func(err error) tea.Msg {
+	return tea.ExecProcess(c, func(err error) tea.Msg {
 		return editorFinishedMsg{err}
 	})
 }