Upper Bound Checker does not use @MinLen annotations

[mernst]

Consider the following code, which is checked in as checker/tests/index/Issue3207.java:

import org.checkerframework.checker.index.qual.LTLengthOf;
import org.checkerframework.common.value.qual.MinLen;

public class Issue3207 {

  void m(int @MinLen(1) [] arr) {
    @LTLengthOf("arr") int j = 0;
  }

  void m2(int @MinLen(1) [] @MinLen(1) [] arr) {
    @LTLengthOf("arr[0]") int j = 0;
  }

  void m3(int @MinLen(1) [] @MinLen(1) [] arr) {
    int @MinLen(1) [] arr0 = arr[0];
    @LTLengthOf("arr0") int j = 0;
  }
}

The Index Checker issues the following error for method m2:

Issue3207.java:15: error: [assignment.type.incompatible] incompatible types in assignment.
        @LTLengthOf("arr[0]") int j = 0;
                                      ^
  found   : @UpperBoundUnknown int
  required: @LTLengthOf(value="arr[0]") int
1 error

I believe the problem is in UpperBoundVisitor.relaxedCommonAssignment. Its documentation lists two heuristics, but the first one seems to apply only to NEW_ARRAY expressions rather than all expressions of type @MinLen(...).