Add a dont-check-error-annotations to compiletest

[BoxyUwU]

cc @jieyouxu

It would be nice if compiletest could support a //@ dont-check-error-annotations annotation that would not require you to annotate your file with //~^ ERROR: anywhere. This would be useful for cases where I only care that the test doesn't start ICEing. Ideally we'd never need this but sometimes I wind up with hundreds of errors with useless spans and it's just not realistic (or helpful) to annotate it all. See for example this test, all the error annotations are in the wrong place as macro diagnostics emit the error on the macro definition not the caller. This means that we'd wind up with ~100 error annotations on the insides of the macros which is not a helpful assertion whatsoever.

[jieyouxu]

Somewhat related is also #46667.