Smithy generator for paginator

[kai-ion]

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Description of changes:
Smithy-based code generator for paginators

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[sbaluja]

Being a bit nitpicky but Instead of manually opening and closing namespace blocks, why don't we do something like this:

public CppWriter writeNamespaceOpen(String namespace) {
        writer.openBlock("namespace $L\n{", namespace);
        return this;
 }

and the same for writeNamespaceClose, but with writer.closeBlock. Its functionally the exact same (block functions indent/dedent which doesn't matter since we clang format anyway) , but we should try to use these functions when opening/closing blocks