Fix #16268: classify IDisposable in type-occurrence positions as Interface, not DisposableType

[T-Gro]

Description

Fixes #16268

When a type like IDisposable appears in a type-occurrence position (e.g., type annotations, interface implementations), it was being classified as DisposableType instead of Interface. This caused incorrect semantic highlighting in editors.

Changes

• src/Compiler/Service/SemanticClassification.fs: In the type-occurrence classification logic, check isInterfaceTy before isDisposableTy. If the type is an interface (like IDisposable), classify it as Interface rather than falling through to the DisposableType check.
• ** ests/FSharp.Compiler.ComponentTests/Language/SemanticClassificationRegressions.fs**: Added regression tests verifying that IDisposable and other interface types in type annotations are correctly classified as Interface.

[github-actions]

❗ Release notes required

@T-Gro,

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[T-Gro]

Review: Looks good — clean, correct fix with solid test coverage.

The fix: Reordering isInterfaceTy before isDisposableTy is the right approach. Interface types (including IDisposable itself) should always be classified as Interface in semantic classification — the DisposableType classification is meant for concrete classes that implement IDisposable, not for interface types that happen to extend it.

Tests: Good coverage across four distinct scenarios: interface impl position, concrete disposable class (negative test guarding against regression), type constraint usage, and a custom non-IDisposable interface.

Minor nit (non-blocking): The test file is missing a trailing newline (the diff shows \ No newline at end of file).