Fix variable rules - variables are not detected when used in lists and object fields

[michaelstaib]

Add more tests

it('variable not used by unreferenced fragment', () => {
expectFailsRule(
NoUnusedVariables,
query Foo($b: String) { ...FragA } fragment FragA on Type { field(a: $a) } fragment FragB on Type { field(b: $b) },
[unusedVar('b', 'Foo', 2, 17)],
);
});

it('variable not used by fragment used by other operation', () => {
expectFailsRule(
NoUnusedVariables,
query Foo($b: String) { ...FragA } query Bar($a: String) { ...FragB } fragment FragA on Type { field(a: $a) } fragment FragB on Type { field(b: $b) },
[unusedVar('b', 'Foo', 2, 17), unusedVar('a', 'Bar', 5, 17)],
);
});