Rust: Improve and rename Adt class

[paldepind]

This PR:

• Moves member predicates that Struct, Enum, and Union have in common to their common superclass Adt. This makes the class much more useful.
• Renames the Adt class to TypeItem. Here's a few reasons, that I think TypeItem addresses:
  • The abbreviation is potentially misleading. Our documentation states that it's for "abstract data type", but I'm pretty sure "algebraic data type" is what's intended in the original rust.ungram.
  • Rust types aren't necessarily abstract, it depends on whether fields/variants are made public.
  • I don't think "algebraic data type" is correct either, as union is included which strictly speaking isn't an algebraic type.
  • It's a pretty terse class name.

[Copilot]

Pull request overview

This PR renames the Adt class to TypeItem and refactors it to move common member predicates (attrs, generic_param_list, name, visibility, where_clause) from the individual subclasses (Struct, Enum, Union) to their common superclass. This improves code reusability and makes the class name more descriptive, as it represents items that define types rather than strictly algebraic data types.

Key changes:

• Renamed Adt class to TypeItem throughout the codebase
• Moved common predicates from Struct, Enum, and Union to TypeItem superclass
• Updated database schema relations to consolidate duplicated table definitions
• Provided upgrade/downgrade scripts for database migration

Reviewed changes

Copilot reviewed 23 out of 40 changed files in this pull request and generated no comments.

Show a summary per file

File	Description
rust/schema/ast.py	Renamed Adt to TypeItem in base class definitions
rust/schema/annotations.py	Added common predicates to TypeItem annotation and dropped them from subclasses
rust/ql/lib/rust.dbscheme	Consolidated common relations into type_item_* tables, removed duplicates
rust/ql/lib/upgrades/e54d01f67a416b3d6eb7b970f27295097f2cac7f/*	Database upgrade scripts for the schema migration
rust/downgrades/c467bf63916002287b7bde8ce8b094c57579bd81/*	Database downgrade scripts for rollback capability
rust/ql/lib/codeql/rust/elements/*	Updated QL library files to use new TypeItem class
rust/ql/test/extractor-tests/macro-expansion/test.ql	Updated test to use TypeItem instead of Adt
rust/extractor/src/*	Updated Rust extractor code to use TypeItem

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[hvitved]

Great change!

[hvitved]

revert