presubmit-check the use of DECLARE_FACTORY for each DEFINE_FACTORY

[alyssawilk]

E-M apparently depends on the former and nothing checks on it upstream :-(

[alyssawilk]

cc @Augustyniak @snowp @phlax

[snowp]

To make things a tad more complicated, EM only relies on DECLARE_FACTORY for things that need to be "force initialized", which is basically just a linker trick to get iOS to include the TUs. For stuff that uses a factory pattern in common code but doesn't rely the extension build system this may not be necessary

That said, enforcing this everywhere probably wouldn't hurt

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