meter element should have the default role=slider with aria-readonly=true

[jongund]

Am not as sure bout this issue, but meter element has the same range requirements as slider, except the value cannot be changed by the user. The aria-invalid could also be set to true if the value of the meter exceeds the high limit or is less than the lower limit.

[stevefaulkner]

@jongund the role etc is not defined here it is defined in the HTML AAM https://w3c.github.io/html-aam/#el-meter which is currently in a state of flux in this regard.

[scottaohara]

closing this issue since meter will map to role=meter and not slider