Fix TypeUtils.isAssignable() for wildcards with multiple upper bounds

[Alwaysgaurav1]

Description

Fixes an issue in TypeUtils.isAssignable(Type, WildcardType, Map) where checking assignability of a WildcardType with multiple upper bounds (intersection types such as ? extends Serializable & Cloneable) to another WildcardType (such as ? extends Serializable) incorrectly returned false.

Root Cause

When the subject type is a WildcardType, the upper bounds loop previously enforced that every upper bound in the subject wildcard had to be assignable to each target upper bound toBound (forall bound in upperBounds: isAssignable(bound, toBound)):

for (Type toBound : toUpperBounds) {
    toBound = substituteTypeVariables(toBound, typeVarAssigns);
    for (final Type bound : upperBounds) {
        if (!isAssignable(bound, toBound, typeVarAssigns)) {
            return false;
        }
    }
}

[Alwaysgaurav1]

@garydgregory, please review it quickly.