Prefer implicit {} over explicitly declared {} in subtype reduction

[ahejlsberg]

Fixes #1563.

[Copilot]

Pull Request Overview

This PR fixes issue #1563 by improving TypeScript's subtype reduction algorithm to prefer implicit empty object types ({}) over explicitly declared empty object types in union types. The change addresses a type checking discrepancy where v || {} was incorrectly being assigned the explicitly declared empty object type instead of the implicit one.

Key changes:

• Added logic in the subtype reduction algorithm to prioritize implicit empty object types
• Added a comprehensive test case to verify the fix

Reviewed Changes

Copilot reviewed 5 out of 5 changed files in this pull request and generated no comments.

Show a summary per file

File	Description
testdata/tests/cases/compiler/implicitEmptyObjectType.ts	New test case demonstrating the issue with unknown || {} type assignment
testdata/baselines/reference/compiler/implicitEmptyObjectType.types	Expected type output showing v || {} resolves to {} type
testdata/baselines/reference/compiler/implicitEmptyObjectType.symbols	Expected symbol resolution baseline for the test
testdata/baselines/reference/compiler/implicitEmptyObjectType.errors.txt	Expected error output showing type assignment error
internal/checker/checker.go	Core fix in subtype reduction to prefer implicit empty object types

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