Multi-Value Support for Binary DocValues [LUCENE-10666]

#11690 introduces a binary doc value format for shapes. Since the geometries are decomposed into triangles the binary docvalue encoding can technically support multi shapes and geometry collections in a single doc value format, however it feels this is hacking around the limitation of supporting multi-values for binary doc values. With multi-value binary individual geometries can be stored in their own binary doc value w/ multiple binary per doc. I'd like to open this issue to explore adding multi-value support to binary doc values. Are there concerns, limitations, traps?

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Migrated from [LUCENE-10666](https://issues.apache.org/jira/browse/LUCENE-10666) by Nick Knize (@nknize), 2 votes, updated Jul 29 2022

Review #11690 and the binary DocValues format for shapes, then compare the single-value and proposed multi-value cases described here. The issue is exploratory, so begin by identifying the API, format, and limitation questions; it is done only when a concrete implementation target and acceptance criteria are agreed.

Written by the indexing model from the issue text.