Tests whether the component is in the read-only mode. The user can not
change the value of a read-only component. As only
AbstractFieldor
LegacyField components normally have a value that can be input
or changed by the user, this is mostly relevant only to field components,
though not restricted to them.
Notice that the read-only mode only affects whether the user can change
the value of the component; it is possible to, for example, scroll
a read-only table.
The method will return
true if the component or any of its
parents is in the read-only mode.