`map.get(@PolyDet)` should return `@PolyDet`, for `@Det` or `@OrderNonDet` map

[mernst]

I expect the following code to type-check:

import java.util.HashMap;
import java.util.LinkedHashMap;
import org.checkerframework.checker.determinism.qual.*;

public class MapGetPoly {

    private static @Det LinkedHashMap<String, Integer> map1 = new @Det LinkedHashMap<>(8);

    private static @OrderNonDet HashMap<String, Integer> map2 = new @OrderNonDet HashMap<>(8);

    public static @PolyDet Integer myGet1(@PolyDet String key) {
        return map1.get(key);
    }

    public static @PolyDet Integer myGet2(@PolyDet String key) {
        return map2.get(key);
    }
}

However, the Determinism Checker issues the following errors:

MapGetPoly.java:9: error: [ordernondet.on.noncollection.and.nonarray] @OrderNonDet annotation is invalid for non-collections and non-arrays
    private static @OrderNonDet HashMap<String, Integer> map2 = new @OrderNonDet HashMap<>(8);
                                                         ^
MapGetPoly.java:12: error: [argument.type.incompatible] incompatible argument for parameter arg0 of get.
        return map1.get(key);
                        ^
  found   : @PolyDet String
  required: @Det Object
MapGetPoly.java:16: error: [argument.type.incompatible] incompatible argument for parameter arg0 of get.
        return map2.get(key);
                        ^
  found   : @PolyDet String
  required: @Det Object
MapGetPoly.java:16: error: [method.invocation.invalid] call to get(java.lang.Object) not allowed on the given receiver.
        return map2.get(key);
                       ^
  found   : @OrderNonDet HashMap
  required: @Det HashMap
4 errors

The error on line 9 is tracked in #211; this issue is about the three errors at the invocations of Map.get.