Improved consistency of @ inferred with other test macros

[c42f]

As a heavy user of @inferred I'd like it to be a little more user friendly and consistent with the other testing macros. My main gripe is that it's a test in its own right; I'd like to be able to write @test_inferred f(x) and have it register with the current test set, rather than unilaterally throwing an exception on failure.

The @test_warn macro does exactly this, and also returns the result so that it can be composed with @test if desired:

@test (@test_warn "deprecated" num2hex(1)) == "0000000000000001"

See related discussion over at: #20348 (comment)

I think there's two separate decisions here:

1. Make @inferred register the result with the current test set
2. If this is done, consider renaming to @test_inferred for consistency with other testing macros.

[c42f]

Original discussion around @inferred: #5404

[fredrikekre]

Related: #21098