As a part of the maintenance, we ought to migrate to the `hydrate` method the next blocks which are currently using the `frontendRendered` when saved.

• Counter (migrated through #1099)
• Gallery (migrated through #932)
• GuestBook (migrated through #1105)
• Timeline (migrated through #1118)
• ENForm (migrated through #1119)
• Covers (migrated through #1104)
• Split Two Columns (migrated through #1131)
• Articles (migrated through #1137)
• Spreadsheet (migrated through #1102)

Maybe another block is missing from that list.

These method has been deprecated 13 months ago through #652.