Fix EZP-21585: set correct col. length for oracle

I detail: properly declare all oracle columns lengths using CHAR semantics, to allow for UTF8.
While at it, set the length for all BLOBS we shorten to 4k instead of arbitrary 3000 or 3100

Meant to replace both https://github.com/ezsystems/ezoracle/pull/18 and https://github.com/ezsystems/ezpublish-legacy/pull/811