Fixes Mojo alias highlighting in VS Code by post-processing semantic tokens returned from LSP server

[simutisernestas]

The LSP currently resolves aliases like Some for hover, but emits them as variable semantic tokens. This patch reclassifies variable tokens as type only when they appear in syntactic type positions, such as:

• parameter annotations: writer: Some[Writer]
• variable annotations: var x: MyAlias
• return annotations: -> MyAlias
• trait/inheritance lists: struct Foo(Copyable, Writable)

A minimal regression test was added for the semantic-token correction behavior.

Note that, this is an extension-side workaround. The more correct long-term fix should likely live in mojo-lsp-server, which has the semantic information needed to classify aliases directly as type-like semantic tokens instead of variable.

[github-actions]

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[simutisernestas]

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[simutisernestas]

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