Attaching Warnings discards the 'hidden part' of an intersection type

[radeusgd]

As requested by @JaroslavTulach, reporting this as a separate issue.

Whenever an intersection type A & B is cast to A (hiding the B part), the B part should still be possible to be uncovered by a cast. However attaching a warning to a value makes it impossible to do so.

We already have pending tests demonstrating the issue:

enso/test/Base_Tests/src/Semantic/Multi_Value_As_Type_Refinement_Spec.enso

Lines 297 to 334 in 54ccd1a

	group_builder.specify "attaching warnings to an intersection type should not lose even the hidden refinements" pending=dispatch_pending <|
	ab = make_a_and_b
	x = ab:A
	x_with_warning = Warning.attach (Illegal_State.Error "my warning") x
	y = x_with_warning:(A & B)
	y.is_a A . should_be_true
	y.is_a B . should_be_true
	y.a_method . should_equal "A method"
	y.b_method . should_equal "B method"
	Problems.expect_only_warning Illegal_State y
	group_builder.specify "removing warnings from an intersection type should not lose even the hidden refinements" pending=dispatch_pending <|
	ab = make_a_and_b
	x1 = Warning.attach (Illegal_State.Error "my warning") (ab:A)
	x2 = (Warning.attach (Illegal_State.Error "my warning") ab):A
	x1_without_warning = x1.remove_warnings
	x2_without_warning = x2.remove_warnings
	r1 = x1_without_warning:(A & B)
	r2 = x2_without_warning:(A & B)
	Problems.assume_no_problems r1
	r1.is_a A . should_be_true
	r1.is_a B . should_be_true
	r1.a_method . should_equal "A method"
	r2.b_method . should_equal "B method"
	Problems.assume_no_problems r2
	r2.is_a A . should_be_true
	r2.is_a B . should_be_true
	r2.a_method . should_equal "A method"
	r2.b_method . should_equal "B method"
	r3 = (ab:A).remove_warnings:(A & B)
	r3.is_a A . should_be_true
	r3.is_a B . should_be_true
	r3.a_method . should_equal "A method"
	r3.b_method . should_equal "B method"