[lldb] Mark most SBAPI methods involving private types as protected or private

Many SB classes have public constructors or methods involving types that
are private. Some are more obvious (e.g. containing lldb_private in the
name) than others (lldb::FooSP is usually std::shared_pointer<lldb_private::Foo>).

This commit explicitly does not address FileSP, so I'm leaving that one
alone for now.

Some of these were for other SB classes to use and should have been made
protected/private with a friend class entry added. Some of these were
public for some of the swig python helpers to use. I put all of those
functions into a class and made them static methods. The relevant SB
classes mark that class as a friend so they can access those
private/protected members.

I've also removed an outdated SBStructuredData test (can you guess which
constructor it was using?) and updated the other relevant tests.

Differential Revision: https://reviews.llvm.org/D150157