Removes all objects from this list; the length of the list becomes zero.
Throws an UnsupportedError, and retains all objects, if this is a fixed-length list.
Source
/**
* Removes all objects from this list;
* the length of the list becomes zero.
*
* Throws an [UnsupportedError], and retains all objects, if this
* is a fixed-length list.
*/
void clear();