fix: ensure $store reads are properly transformed

[dummdidumm]

The backing store variable of a $store read could be a variable that itself needs a transformer, which is why we need to move the setup of the store transformers to the end of the chain

fixes #12859

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[Rich-Harris]

I think we can fix this more simply — rather than being careful about the order in which transformers are added (it shouldn't matter), we just avoid transforming the store binding eagerly. Opened #12952

[dummdidumm]

Closing in favor of #12952