vaadin-text-area style in readonly mode

[gatanaso]

The vaadin-text-area styles are not being applied correctly when it’s in readonly mode.
There is no dashed border, or a transparent background as it is the case for the vaadin-text-field

1. Expected behavior:
   The vaadin-text-area has a dashed border and transparent background when in readonly mode, such as:

2. Actual behavior:
   The vaadin-text-area has no borders and the background is not transparent:

[web-padawan]

Caused by this line: https://github.com/vaadin/vaadin-text-field/blob/master/theme/lumo/vaadin-text-area-styles.html#L18

Should be fixed if we change to this one:

:host(:not([readonly])) [part="input-field"]::after {