feat: polymorphic join querying by fields that don't exist in every collection (#12648)

This PR makes it possible to do polymorphic join querying by fields that
don't exist in all collections specified in `field.collection`, for
example:
```
const result = await payload.find({
  collection: 'payload-folders',
  joins: {
    documentsAndFolders: {
      where: {
        and: [
          {
            relationTo: {
              in: ['folderPoly1', 'folderPoly2'],
            },
          },
          {
            folderPoly2Title: { // this field exists only in the folderPoly2 collection, before it'd throw a query error.
              equals: 'Poly 2 Title',
            },
          },
        ],
      },
    },
  },
})
```

---------

Co-authored-by: Jarrod Flesch <jarrodmflesch@gmail.com>