Positive coverage: prove_wc / alias eq

1 test exercised this rule:

Source location: tests/projection.rs:115

#[test]
fn projection_equality() {
    test_where_clause(
        PROJECTION_EQUALITY,
        "exists<U> {} => { Trait1(S), <S as Trait1<>>::Type = U }",
    )
    .assert_ok(expect_test::expect!["{Constraints { env: Env { variables: [?ty_1], bias: Soundness, pending: [], allow_pending_outlives: false }, known_true: true, substitution: {?ty_1 => u32} }, Constraints { env: Env { variables: [?ty_1], bias: Soundness, pending: [], allow_pending_outlives: false }, known_true: true, substitution: {?ty_1 => <S as Trait1>::Type} }}"]);

    test_where_clause(PROJECTION_EQUALITY, "exists<U> {} => { Trait2(S, U) }")
        .assert_ok(expect_test::expect!["{Constraints { env: Env { variables: [?ty_1], bias: Soundness, pending: [], allow_pending_outlives: false }, known_true: true, substitution: {?ty_1 => u32} }, Constraints { env: Env { variables: [?ty_1], bias: Soundness, pending: [], allow_pending_outlives: false }, known_true: true, substitution: {?ty_1 => <S as Trait1>::Type} }}"]);
}