Annotation symbols should ignore icon placement

[brunoabinader]

We currently set icon-allow-overlap to true when creating the annotation symbol layer but we also need icon-ignore-placement set to true.

Ignoring icon placements causes symbol annotations to skip calculating the placement scale - which is currently broken (see #6628) and thus returning the correct values for rendered features.

[mention-bot]

@brunoabinader, thanks for your PR! By analyzing the history of the files in this pull request, we identified @jfirebaugh, @ansis and @boundsj to be potential reviewers.

[jfirebaugh]

Setting setIconIgnorePlacement(true) makes sense, but can you explain the collision_tile.cpp part of this PR?

[brunoabinader]

can you explain the collision_tile.cpp part of this PR?

In CollisionTile, features coming from layers in which placement is ignored - icon-ignore-placement: true - are inserted in the ignoredTree - which ignores placement scale - notice how placement scale is calculated only for features from the tree container.

This means these features are always visible and can bypass the placement scale check.

[brunoabinader]

Addressed @jfirebaugh review comments.