Remap the ~44 extension vtable null-check assertions across host_connector/, shared/handle/, and shared/extension_status.h from ad-hoc tassert codes to ErrorCodes::InvalidExtensionVTable, swapping tassert -> uassert since a missing vtable entry is the extension author's fault, not a server invariant violation. Converts corresponding DEATH_TESTs to ASSERT_THROWS_CODE-style tests. Depends on SERVER-131005 (IDL scaffolding).