Select style multiple select interactions removed

[bepremeg]

This fixes #10486 by removing the event listeners when an
interaction is removed from a map.

[jahow]

Thanks for your contribution! I think a new test would be in order, although your code seems like it should fix the problem. Please let me know if you need indications.

[bepremeg]

I had a look at the existing tests. I'll probably find a way how to test this. But I'm in doubt what the best place is. a top-level describe('replace Select'), something under describe('selecting a polygon'), or another place altogether?

[jahow]

I'd say a top level describe('clear event listeners on interaction removal') would make sense, so at the same level as this:

openlayers/test/spec/ol/interaction/select.test.js

Line 122 in 6e8f340

describe('selecting a polygon', function() {

Thanks

[bepremeg]

All right. I had some trouble finding the right way to test this. I couldn't get my test to fail when I reverted my fix :-(
Turns out that the issue also requires an external feature collection. Obvious in hindsight.
This also requires that the activation of the event listeners only happens when the interaction is added to the map. Otherwise the addFeature is invoked regardless of the interaction being associated with a map or not.
This change also makes the event handler association more symmetrical.

[bepremeg]

@jahow Could you have a look at the test result? There is one failing test for TileQueue on Circleci, but it works on my local test environment and I don't see how my change could impact that test.

[bepremeg]

I now have exactly the same test code as where I started but the build succeeds now.
As far as I'm concerned, this patch is ready.

[mike-000]

@jahow Could you have a look at the test result? There is one failing test for TileQueue on Circleci, but it works on my local test environment and I don't see how my change could impact that test.

Unrelated failed tests seem to be quite common, for example see #7437 (comment) Any change even an edit to a comment will rerun the tests as will squashing and force pushing which also tidies the commit history.

[bepremeg]

@jahow Indeed. The tests are passing now, even if the code is the same. I made a few commits that cancel each other.

[michalzielanski]

if (map) {
    if (!currentMap) {
        // ...
    }
    // ...

is needed.
For such a code:

import Map from 'ol/Map';
import Select from 'ol/interaction/Select';

var map1 = new Map(/* ... */);
var map2 = new Map(/* ... */);

var selectInteraction = new Select();
// Attach interaction to a map1.
selectInteraction.setMap(map1);
// Change map for interaction to map2.
selectInteraction.setMap(map2);

there will be two listeners per event.

[ahocevar]

Rebased; fixed merge conflicts.