feat: make bar & rect marks support bandPosition (allow center-alignm…

…ent with ticks) (vega#9126)

* docs(examples): examples for using bandPosition=0

* chore: update examples [CI]

* fix: calculate offseted rect position for timeUnit if bandPosition != 0.5

* fix: use offsetted rect position in aggregate

* fix: use offsetted rect in mark position

* fix: use offsetted rect in scale domain

* fix: correctly read default bandPosition

* fix: apply bandOffset to grouped bars with timeUnit

* chore: update examples [CI]

* style: auto-formatting [CI]

* docs: update docs

* chore: update TOC [CI]

---------

Co-authored-by: GitHub Actions Bot <vega-actions-bot@users.noreply.github.com>

examples/compiled/bar_binned_yearmonth_grouped_center_band.vg.json

@@ -0,0 +1,171 @@
+{
+  "$schema": "https://vega.github.io/schema/vega/v5.json",
+  "description": "Stock price over time.",
+  "background": "white",
+  "padding": 5,
+  "width": 200,
+  "height": 200,
+  "style": "cell",
+  "data": [
+    {
+      "name": "source_0",
+      "url": "data/stocks.csv",
+      "format": {"type": "csv", "parse": {"date": "date"}},
+      "transform": [
+        {
+          "type": "filter",
+          "expr": "inrange(time(datum[\"date\"]), [time(datetime(2005, 0, 1, 0, 0, 0, 0)), time(datetime(2005, 2, 1, 0, 0, 0, 0))])"
+        },
+        {
+          "type": "formula",
+          "expr": "timeOffset('month', datum['date'], 1)",
+          "as": "date_end"
+        },
+        {
+          "type": "formula",
+          "expr": "0.5 * timeOffset('month', datum['date'], -1) + 0.5 * datum['date']",
+          "as": "date_offsetted_rect_start"
+        },
+        {
+          "type": "formula",
+          "expr": "0.5 * datum['date'] + 0.5 * datum['date_end']",
+          "as": "date_offsetted_rect_end"
+        },
+        {
+          "type": "stack",
+          "groupby": ["date", "symbol"],
+          "field": "price",
+          "sort": {"field": [], "order": []},
+          "as": ["price_start", "price_end"],
+          "offset": "zero"
+        },
+        {
+          "type": "filter",
+          "expr": "(isDate(datum[\"date\"]) || (isValid(datum[\"date\"]) && isFinite(+datum[\"date\"]))) && isValid(datum[\"price\"]) && isFinite(+datum[\"price\"])"
+        }
+      ]
+    }
+  ],
+  "marks": [
+    {
+      "name": "marks",
+      "type": "rect",
+      "style": ["bar"],
+      "from": {"data": "source_0"},
+      "encode": {
+        "update": {
+          "fill": {"scale": "color", "field": "symbol"},
+          "ariaRoleDescription": {"value": "bar"},
+          "description": {
+            "signal": "\"date: \" + (timeFormat(datum[\"date\"], timeUnitSpecifier([\"year\",\"month\"], {\"year-month\":\"%b %Y \",\"year-month-date\":\"%b %d, %Y \"}))) + \"; price: \" + (format(datum[\"price\"], \"\")) + \"; symbol: \" + (isValid(datum[\"symbol\"]) ? datum[\"symbol\"] : \"\"+datum[\"symbol\"])"
+          },
+          "xc": {
+            "scale": "x",
+            "field": "date",
+            "offset": {"scale": "xOffset", "field": "symbol", "band": 0.5}
+          },
+          "width": {"signal": "max(0.25, bandwidth('xOffset'))"},
+          "y": {"scale": "y", "field": "price_end"},
+          "y2": {"scale": "y", "field": "price_start"}
+        }
+      }
+    }
+  ],
+  "scales": [
+    {
+      "name": "x",
+      "type": "time",
+      "domain": {
+        "data": "source_0",
+        "fields": ["date_offsetted_rect_start", "date_offsetted_rect_end"]
+      },
+      "range": [0, {"signal": "width"}]
+    },
+    {
+      "name": "y",
+      "type": "linear",
+      "domain": {"data": "source_0", "fields": ["price_start", "price_end"]},
+      "range": [{"signal": "height"}, 0],
+      "nice": true,
+      "zero": true
+    },
+    {
+      "name": "xOffset",
+      "type": "band",
+      "domain": {"data": "source_0", "field": "symbol", "sort": true},
+      "range": [
+        {
+          "signal": "-0.4 * (scale('x', datetime(2001, 1, 1, 0, 0, 0, 0)) - scale('x', datetime(2001, 0, 1, 0, 0, 0, 0)))"
+        },
+        {
+          "signal": "0.4 * (scale('x', datetime(2001, 1, 1, 0, 0, 0, 0)) - scale('x', datetime(2001, 0, 1, 0, 0, 0, 0)))"
+        }
+      ]
+    },
+    {
+      "name": "color",
+      "type": "ordinal",
+      "domain": {"data": "source_0", "field": "symbol", "sort": true},
+      "range": "category"
+    }
+  ],
+  "axes": [
+    {
+      "scale": "x",
+      "orient": "bottom",
+      "gridScale": "y",
+      "grid": true,
+      "tickCount": {"signal": "ceil(width/40)"},
+      "tickMinStep": {
+        "signal": "datetime(2001, 1, 1, 0, 0, 0, 0) - datetime(2001, 0, 1, 0, 0, 0, 0)"
+      },
+      "domain": false,
+      "labels": false,
+      "aria": false,
+      "maxExtent": 0,
+      "minExtent": 0,
+      "ticks": false,
+      "zindex": 0
+    },
+    {
+      "scale": "y",
+      "orient": "left",
+      "gridScale": "x",
+      "grid": true,
+      "tickCount": {"signal": "ceil(height/40)"},
+      "domain": false,
+      "labels": false,
+      "aria": false,
+      "maxExtent": 0,
+      "minExtent": 0,
+      "ticks": false,
+      "zindex": 0
+    },
+    {
+      "scale": "x",
+      "orient": "bottom",
+      "grid": false,
+      "title": "date",
+      "format": {
+        "signal": "timeUnitSpecifier([\"year\",\"month\"], {\"year-month\":\"%b %Y \",\"year-month-date\":\"%b %d, %Y \"})"
+      },
+      "labelFlush": true,
+      "labelOverlap": true,
+      "tickCount": {"signal": "ceil(width/40)"},
+      "tickMinStep": {
+        "signal": "datetime(2001, 1, 1, 0, 0, 0, 0) - datetime(2001, 0, 1, 0, 0, 0, 0)"
+      },
+      "zindex": 0
+    },
+    {
+      "scale": "y",
+      "orient": "left",
+      "grid": false,
+      "title": "price",
+      "labelOverlap": true,
+      "tickCount": {"signal": "ceil(height/40)"},
+      "zindex": 0
+    }
+  ],
+  "legends": [{"fill": "color", "symbolType": "square", "title": "symbol"}]
+}