diagnostic testing: need revison to overlapping_spans test that still surfaces under NLL

[pnkfelix]

The test overlapping_spans is deliberately trying to create a bug where two "distinct" spans that happen to overlap will be reported by the diagnostic tool, to test our ability to render them in different styles so that the end user can distinguish them.

Look, its easier if you just see the output from AST-borrowck:

rust/src/test/ui/codemap_tests/overlapping_spans.stderr

Lines 4 to 8 in 2e104a7

	LL | S {f:_s} => {} //~ ERROR cannot move out
	| ^^^^^--^
	| | |
	| | hint: to prevent move, use `ref _s` or `ref mut _s`
	| cannot move out of here

You can see on line 5 the interesting pair of spans combined by using different characters: ^^^^^--^

The problem is that NLL currently happens to not issue such a report with such overlapping spans.

The particular output from NLL right now is the following, but I do not want to categorize that choice of output as a bug in NLL at the moment.

rust/src/test/ui/codemap_tests/overlapping_spans.nll.stderr

Lines 1 to 9 in 746d63a

	error[E0509]: cannot move out of type `S`, which implements the `Drop` trait
	--> $DIR/overlapping_spans.rs:21:14
	|
	LL | S {f:_s} => {} //~ ERROR cannot move out
	| ^^ cannot move out of here
	error: aborting due to previous error
	For more information about this error, try `rustc --explain E0509`.

Thus it fails to exercise the behavior that we are interested in witnessing in this test.

Can someone come up with a test for such overlapping spans that does not rely on vagaries of the borrow checker?

[pnkfelix]

(Coming up with an alternative test may not be an ultra high priority, since the NLL team probably should try to address #51189 )

[pnkfelix]

I'm going to just delete this test as part of resolving #55533. See also #52663 (comment)