[SPARK-53354][CONNECT] Simplify LiteralValueProtoConverter.toCatalystStruct

[heyihong]

What changes were proposed in this pull request?

This PR simplifies the LiteralValueProtoConverter.toCatalystStruct method by refactoring the struct conversion logic to be more straightforward and maintainable. The main changes include:

1. Simplified return type: Changed toCatalystStruct to return only the converted struct value instead of a tuple (Any, proto.DataType.Struct)
2. Extracted struct type resolution: Created a new getProtoStructType method to handle struct type resolution separately
3. Simplified internal conversion: Introduced toCatalystStructInternal method that takes the struct type as a parameter
4. Removed complex type inference logic: Eliminated the LiteralValueWithDataType case class and simplified the getConverter method by removing the inferDataType parameter
5. Enhanced recursive type inference: Improved the getInferredDataType method to support recursive type inference for struct fields

Why are the changes needed?

The original method is a bit overly complex with multiple code paths and conditional logic that made it difficult to understand and maintain. This refactoring improves code readability while preserving the same functionality.

Does this PR introduce any user-facing change?

No. This is a pure refactoring that maintains the same external behavior and API.

How was this patch tested?

build/sbt "connect/testOnly *LiteralExpressionProtoConverterSuite"

Was this patch authored or co-authored using generative AI tooling?

Generated-by: Cursor 1.4.5

[heyihong]

@zhengruifeng

[zhengruifeng]

thanks, merged to master