[Spark] Add Delta Connect Merge Server and Scala Client

[longvu-db]

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Which Delta project/connector is this regarding?

• [X] Spark
• [ ] Standalone
• [ ] Flink
• [ ] Kernel
• [ ] Other (fill in here)

Description

Add support for merge for Delta Connect Server and Scala Client.

The previous PR got reverted since Delta Spark Master testing was broken and Delta Connect's DeltaMergeBuilder was forgotten to be added.

The isSchemaEvolution API was also supposed to be added for Delta Connect in that PR to have feature parity with Delta Classic Scala/Python Client.

How was this patch tested?

Added UTs, tested locally with a checkpoint of Spark Master, the point of time before the Spark commits that broke Delta Spark Master tests were introduced.

Does this PR introduce any user-facing changes?

This PR allows users to do MERGE on Delta Connect (Delta over Spark Connect), so anything that users are able to do with MERGE normally should also be possible with Spark Connect.