Documents / operations > 10mb cause issues

[mikelehen]

@iclems reported this error:

Error: transaction failed: Data returned contains a string greater than 10485760 utf8 bytes in prose… (thrown by Firebase: throw new Error(errorPrefix + "contains a string greater than " + fb.core.util.validation.MAX_LEAF_SIZE_ + " utf8 bytes " + path.toError {snip})
After that, Error: sendOperation() called with invalid operation.

Essentially this means there was an operation (e.g. an insert) greater than 10mb. But this could also have happened when we write a snapshot, where we condense the document into a minimal set of operations. In general, each span of text with unique rich-text attributes will be a separate operation. But if for instance you have no rich-text, the entire document would be one operation. So if the doc is greater than 10mb, it'll fail.