Clean up book keeping and caching of LambdaScopeInfo's

 - Track all the Cached LambdaScopeInfo's so we can delete them in Sema's dtor so that certain PartialDiagnostic::StorageAllocator invariants are maintained and noisy assertions don't occur at the end

 - also patch a fix for a failing deduction : auto x{ { 0, 0 }}; that was creating an assertion failure

 - all clang regressions should now pass ...