[css-inline-3] The behavior when one value is specified for text-box-edge #10703

There was a web developer feedback to the Blink's experimental implementation for when one value is specified.

The current spec says:

If only one value is specified, both edges are assigned that same keyword if possible; else text is assumed as the missing value.

The feedback says, if only one value is specified, to assume the alphabetic under edge instead of text if the over edge is cap or ex, to make it more intuitive.

Does this look like a reasonable change? @fantasai @Clqsin45 @nt1m @argyleink @chrishtr @bfgeek