ODS14: Store (and return via *_LENGTH functions) blob length longer than 4GB

[dyemanov]

This PR contains only ODS-related change (to be merged together with #8401 and #8340). The blh layout has been slightly modified to preserve the blob header size.

The code requires more changes to support bigger BLOBs properly, appropriate PR will be offered later.

[dyemanov]

Answering Vlad's comment inside the commit:

I highly doubt this is required.
IMHO, we should document max blob length as 2 or 4GB and add corresponding checks in code.
This must be properly discussed first.

IMHO, we must store and retrieve blobs of arbitrary size and given that we have them officially (as documented) allowed up to 128GB (IIRC) I see no good excuse to just shrink the documented limit, provided that it costs us nearly nothing.

That said, I'd seriously question the need to process (inside the engine) blobs bigger than 2/4GB. Currently we have a number of functions that read the whole blob contents into memory for processing and it may easily lead to OOM condition even for 4GB blobs. So I'd agree to add some max length for blobs being processed and throw an error for longer blobs. Just not sure whether it should happen everywhere or only in specific places that cannot process blobs chunk-by-chunk.