Write tests for aria-invalid AT value (when validity IDL is set)

[rahimabdi]

When the validity IDL is set, this impacts what ATs should convey for aria-invalid (w3c/aria#2223) so tests should be written when additional test accessors are available. In addition, the validity IDL attribute should not impact attribute reflection for the ariaInvalid IDL attribute, which is being tracked in #177.

Note: As an html-aam issue to be addressed in w3c/aria#2223, it's more accurate to relate aria-invalid with the CSS :invalid pseudo-class here, rather than the validity IDL attribute which reflects the value of :invalid.