[cli] update CLI Output class (#8343)

This commit updates the `Cli::Output` class and the related types. A
new type `OutputImplementer` is added which provides the basic output
functionality, i.e., method `OutputV()`. `Output` class requires a
reference to an `OutputImplementer` which it then uses to provide all
the different `Output{}()` method flavors. The new model allows all
CLI sub-modules to directly inherit `Output` class while reusing a
single and common underlying `OutputImplementer` provided by the
`Cli::Interpreter`.

src/cli/cli_udp.cpp

@@ -43,8 +43,8 @@
 namespace ot {
 namespace Cli {
 
-UdpExample::UdpExample(Output &aOutput)
-    : OutputWrapper(aOutput)
+UdpExample::UdpExample(otInstance *aInstance, OutputImplementer &aOutputImplementer)
+    : Output(aInstance, aOutputImplementer)
     , mLinkSecurityEnabled(true)
 {
     memset(&mSocket, 0, sizeof(mSocket));