refactor(types): remove type_name and sub_fields from Field

[BugenZhao]

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What's changed and what's your intention?

This PR removes type_name and sub_fields from the Field struct.

These two fields are specific to Fields with struct (composite) types.

• type_name only presents if the composite type is from external schema (like Avro definition) and is only used for debugging purposes (like DESCRIBE)

• sub_fields is used for fields of composite types. Note that StructType already contains the information of field name and field type, so the only point of sub_fields is to provide type_name for fields of composite types.

• These 2 fields are poorly maintained in our codebase, because there are multiple constructors and they are not enforced to be initialized.

So I believe deprecating them is a good choice. Ideally, we should embed type_name directly inside StructType (#19538), i.e., the tree structure for the data type, instead of having another tree structure (i.e., sub_fields).

Checklist

• I have written necessary rustdoc comments.
• I have added necessary unit tests and integration tests.
• I have added test labels as necessary.
• I have added fuzzing tests or opened an issue to track them.
• My PR contains breaking changes.
• My PR changes performance-critical code, so I will run (micro) benchmarks and present the results.
• My PR contains critical fixes that are necessary to be merged into the latest release.

Documentation

• My PR needs documentation updates.

Release note

[BugenZhao]

• refactor(types): remove type_name and field_descs from ColumnDesc #20497
• refactor(types): remove type_name and sub_fields from Field #20496 👈 (View in Graphite)
• refactor(types): assign name f{} to unnamed fields of struct (record) #20490
• main

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[xxchan]

type_name only presents if the composite type is from external schema (like Avro definition) and is only used for debugging purposes (like DESCRIBE)

🤣🥵

#17128
#13104

[xxchan]

BTW, what's the current behavior of DESCRIBE after the PR?

[BugenZhao]

BTW, what's the current behavior of DESCRIBE after the PR?

See #20496:

field_descs will be generated on the fly based on the StructType when it's used in DESCRIBE. Resolve #17128.