Text-anchor is not properly supported in collision circle placement

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Collision circle placement logic treats all line labels as they would be always placed directly on a line. This conflicts with the "text-anchor" property which can be used to offset text relative to anchor position. Another issue is that the placement logic ignores the possibility of line labels being upside down. This becomes a problem when the renderer wants to flip a label that is using a non-centered Text-anchor.

**mapbox-gl-js version**: `1.9.0-dev`

### Steps to Trigger Behavior

This issue can be replicated with the following render test or by visiting `debug/textsize.html` page.

style.json

```json

{
"version": 8,
"metadata": {
"test": {
"collisionDebug": true,
"width": 512,
"height": 512
}
},
"center": [
0,
0
],
"zoom": 4,
"pitch": 0,
"bearing": 0,
"sources": {
"geojson": {
"type": "geojson",
"maxzoom": 1,
"data": {
"type": "FeatureCollection",
"features": [{
"type": "Feature",
"properties": {
"name": "abcdefg"
},
"geometry": {
"type": "LineString",
"coordinates": [
[ -5, 4 ], [ 5, 4 ]
]
}

},
{
"type": "Feature",
"properties": {
"name": "abcdefg"
},
"geometry": {
"type": "LineString",
"coordinates": [
[ 5, -4 ], [ -5, -4 ]
]
}

}]
}
}
},
"glyphs": "local://glyphs/{fontstack}/{range}.pbf",
"layers": [
{
"id": "background",
"type": "background",
"paint": {
"background-color": "white"
}
},
{
"id": "line",
"type": "symbol",
"source": "geojson",
"layout": {
"text-field": "{name}",
"text-font": [
"Open Sans Semibold",
"Arial Unicode MS Bold"
],
"symbol-placement": "line",
"symbol-spacing": 100,
"text-pitch-alignment": "map",
"text-anchor": "bottom-right"
}
}
]
}

```

Result of the render test:

Start with the render test described in the issue or the debug/textsize.html page, using the supplied style.json to reproduce the collision circle placement. Trace the line-label placement logic and verify that collision circles account for text-anchor offsets and labels that may be flipped upside down.

Written by the indexing model from the issue text.