[java] UseExplicitTypes: cases where 'var' should be unobjectionable

[StevanWhite]

Is your feature request related to a problem? Please describe.

The rule UseExplicitTypes regarding the Java 10 type var has two properties, allowLiterals and allowCtors.

There are two other legitimate uses of var that I run into often, where the type is obvious:
explicit casts, and iteration over an Iterable whose type is explicit and apparent.
But PMD complains about these, and cramps my style.

Direct cast is still a reasonable construct:

// direct cast
    var other = (MyClass<E>)obj;

An iteration over a Collection whose type is immediately apparent:

    method( List<E> list) {
        for( var e : list ) {
            ...
        }
    }

Generally, iteration over an explicitly-typed Iterable:

    method( Iterable<E> it) {
        for( var e : it ) {
            ...
        }
    }

Describe the solution you'd like

For the rule UseExplicitTypes,

A property allowExplicitCasts, to allow var in the first situation.

A property allowExplicitIterables to allow var in the second situation.

Describe alternatives you've considered

The exact property names aren't important. Those were the best I came up with.

Additional context