Added blobAsText support for text blobs

[MartinKoeditz]

feat: add blobAsText option for BLOB SUB_TYPE TEXT
test: cover blobAsText in shared driver test suite

That way it can simply used be knex-firebird-adapter (and others) for reading text BLOBs.

[MartinKoeditz]

Sample:

import { createNativeClient, getDefaultLibraryFilename } from 'node-firebird-driver-native';

const client = createNativeClient(getDefaultLibraryFilename());

const attachment = await client.connect('/path/to/database.fdb', {
  username: 'SYSDBA',
  password: 'masterkey',
  blobAsText: true,
});