checker: avoid &Type as generic concrete type on usage

[felipensp]

Fix #18440
Fix #18367

🤖 Generated by Copilot at c6065ce

Prevent using reference types as generic concrete types in the compiler. Add a test case and an error message for this scenario.

🤖 Generated by Copilot at c6065ce

• Report and test error when using reference type as generic concrete type (link, link, link)

• Check for ampersand token after opening bracket in parse_type.v and call error_with_pos with message and position (link)
• Add expected compiler error message in wrong_ref_type_as_concrete_err.out suggesting to use generic type parameter instead (link)
• Add test case in wrong_ref_type_as_concrete_err.vv that imports datatypes module, defines heap-allocated struct User, and tries to create doubly linked list of references to User (link)

[Delta456]

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