Allow (is) & (every_is) simultaneously

[dmdashenkov]

Consider options (is) and (every_is) applied to a type at the same time:

option (every_is).java_type = "Fruit";

message Tomato {
    option (is).java_type = "Vegetable";

    // ...
}

Currently, Java class Tomato only implements Vegetable interface.

With this PR we make (is) and (every_is) complementary. This way, Java class Tomato implements both Vegetable and Fruit interfaces.

[codecov]

Codecov Report

Merging #531 into master will decrease coverage by 0.00%.
The diff coverage is 100.00%.

@@             Coverage Diff              @@
##             master     #531      +/-   ##
============================================
- Coverage     73.70%   73.70%   -0.01%     
+ Complexity     2931     2930       -1     
============================================
  Files           503      503              
  Lines         11872    11871       -1     
  Branches        668      667       -1     
============================================
- Hits           8750     8749       -1     
  Misses         2902     2902              
  Partials        220      220              

[dmdashenkov]

@armiol, PTAL.

[armiol]

@dmdashenkov do we test this behavior?