Implement List's any() function

This is needed for cases where we only need to know if a list item
matches the given predicate (eg. in Servo, we need to know if attributes
from different DOM elements are equal).
auto merge of #12132 : brunoabinader/rust/list-matches-predicate, r=alexcrichton

This is needed for cases where we only need to know if a list item matches the given predicate (eg. in Servo, we need to know if attributes from different DOM elements are equal).