Implement template parameter resolution for type completions

[bangbangsheshotmedown]

- vibe coded -

Implement template parameter resolution for type completions

When completing members of templated types (e.g., Data!Vec2), DCD now resolves template parameters (T) to their concrete arguments (Vec2), providing accurate type information for autocomplete suggestions.

Changes:

• Add templateInstantiation lookup kind to track template instantiations
• Parse template arguments from TypeIdentifierPart AST nodes
• Store template arguments in TypeLookup for use in type resolution
• Implement resolveTemplateInstantiation() to substitute template parameters
• Add tc_templates test case to verify template resolution

Fixes: Code completion for templated structs/classes where members use template parameters in their type declarations.

[github-actions]

Thanks for your Pull Request and making D better!

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[bangbangsheshotmedown]

Failures seems unrelated to the PR