fix(ngAria): handle non-string model values

Fix for #10212. Compare the string value of the model
so that aria-checked will be properly applied to
type=radio in the case where the model is a number

Closes #10212
Actually, `'' + newval` will still throw in the Object.create(null) case, although that is a bit of a corner case.

Maybe `val && val.toString ? val.toString() : val` would work better.