Introduce a shared test-types library to remove copy-pasted type definitions across e2e tests

Several e2e tests independently define the same set of types often along with the same trait and impls. This is pure copy-paste, kept in sync by hand, which is error-prone and noisy to maintain.

E.g., we have this situation in many of the tests for references and also in the three tests used in #7692:
• test/src/e2e_vm_tests/test_programs/should_pass/language/match_expressions_enums_zero_sized_variants
• test/src/e2e_vm_tests/test_programs/should_pass/language/const_eval
• test/src/e2e_vm_tests/test_programs/should_pass/language/enum_zero_sized_variants

Proposal is to create a common library project (e.g. test/src/e2e_vm_tests/test_programs/common_test_types, or reuse the existing in-language test_types pattern) that exports these shared types and traits, and have tests depend on it instead of redefining everything locally.