Add multirange support

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Multirange objects introduced in PostgreSQL 14.

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Catalog inspection and builtin multirange metadata is already in.

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The multirange binary format is:

• 4 bytes: number of elements:
• for each element:
  • 4 bytes range binary representation length
  • range as dumped on its own

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The multirange text format is similar to the array one, with {} delimiters and comma-separated entries. However the entries are not double-quoted even if they contain a comma.