Add proper deprecation for classes renamed in OpalCompiler

[JanBliznicenko]

During Pharo 13 development, many AST and IB classes got prefix OC, like ASTMethodNode becoming OCMethodNode and IBMethod becoming OCIBMethod.
While AST-Core classes have deprecation rules set in BaselineOfBasicTools>>#postload:package: using deprecatedAliases:, there is no deprecation system applied on renamed classes in OpalCompiler-Core, like IRMethod renamed to OCIRMethod, causing any projects that subclass or extend classes like IRMethod not to load in Pharo 13, requiring manual changes in text editor outside of Pharo.

[Ducasse]

I like this script

makeDeprecatedClassAliases

    <script>
    self withAllSubclassesDo: [ :class |
        | deprecatedClass |
        deprecatedClass := (class name allButFirst: 2) asSymbol.
        class deprecatedAliases: { deprecatedClass } ]