Cosmos: Redo ReadItem and partition key management

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• Rewrote partition key & read item detection to operate as the final postprocessing step, pattern-matching on the final SQL tree, rather than on incoming pre-translated LINQ expressions. This removes the need to pattern-match each and every construct (== and Equals, EF.Property, indexer properties...), and simply performs the transformation whenever the final SQL form is compatible.
• Implemented ReadItem transformation rules for hierarchy vs. shared containers; we no longer transform to ReadItem for base types in a hierarchy.
• Unified the partition key management & flow schemes (we had no less than three). Now regardless of how the partition key is found/managed (WithPartitionKey(), predicate comparison extraction, ReadItem), the values are simply set on CosmosQueryCompialtionContext.PartitionKey.
• Improved WithPartitionKey() for better support for parameterizing partition key properties: previously [NonParameterized] was used, causing us to recompile queries with different WithPartitionKey arguments. We now properly parameterize and use a single compilation.
• Move WithPartitionKey() processing from preprocessing to translation (so that we can get Sql{Constant,Parameter}Expression)
• Brought across SqlExpressionFactory optimizations that have recently been done in relational

Closes #20693
Closes #20350
Fixes #34085
Fixes #33960

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This caused us to recompile the query for each different constant value of a partition key passed to WithPartitionKey()... We now support proper parameterization.