Redefine defs when constant and number in generic arguments are equal

[HertzDevil]

This PR makes the following two defs redefinitions of each other:

class Foo(N); end
X = 1

def foo(x : Foo(1)); end
def foo(x : Foo(X)); end

The same already happens if X were an alias type:

class Foo(T); end
alias X = Int32

# redefinitions
def foo(x : Foo(Int32)); end
def foo(x : Foo(X)); end

Except that only exact matches are allowed here; X's initializer must be exactly the NumberLiteral 1, not an expression like 4 - 3. (Those expressions still work during method lookup, just not during overload ordering.)

[Sija]

Style related suggestion.

Suggested change

	return false if self_free_vars && self.single_name?.try { |name| self_free_vars.includes?(name) }
	return false if self_free_vars && self.single_name?.try &.in?(self_free_vars) }