Adds support for references by combining two approaches:

1. Where anything included in _callable_variable is used directly, we wrap it in by_ref
2. Where there is a wrapping container already (or where by_ref simply doesn't make sense, like function returns) we apply the reference_modifier field

One new conflict has been added to disambiguate array creation and array destructing.

Also: Fixes float without decimal parts (but with trailing .)

Checklist:

• All tests pass in CI
• There are sufficient tests for the new fix/feature
• Grammar rules have not been renamed unless absolutely necessary (0 rules renamed)
• The conflicts section hasn't grown too much (1 new conflicts)
• The parser size hasn't grown too much (master: 2595, PR: 2624)