feature #2547 [Map] markers, polygons and polylines removal (sblondeau)

This PR was merged into the 2.x branch.

Discussion
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[Map] markers, polygons and polylines removal

| Q             | A
| ------------- | ---
| Bug fix?      | no
| New feature?  | yes <!-- please update src/**/CHANGELOG.md files -->
| Issues        | Fix #... <!-- prefix each issue number with "Fix #", no need to create an issue if none exist, explain below instead -->
| License       | MIT

Add new methods to remove markers, polygons or polylines (map elements)
Map elements will be store in SplObjectStorage instead of arrays.

When create a map element, you can now add an optional identfier (string).
New methods `getMarker(string identifier)`, `getPolygon(string identifier)` and `getPolyline(string $identifier)` car retreive a map element from its identfiier.

example
    $departureMarker = new Marker (
        position: new Point(45.7640, 4.8357),
        title: 'Lyon',
        identifier: 'departure'
    )

    $map->addMarker($departureMarker);

    // remove marker with
    $map->removeMarker($departureMarker)
    // or
    $map->removeMarker($map->getMarker('departure'));

Commits
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e19fff9 [Map] Add dedicated methods to remove Marker, Polygon and Polyline instances from a Map

Author: Kocal