Marker does not render correctly for full-block FieldColour fields

[cpcallen]

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Component

@blockly/field-colour

Description

When using the Zelos renderer, certain fields (notably: FieldColour) are rendered as full-block fields. When the marker is moved to such a field, it disappears.

Initial investigation suggests the issue is that the field has zero width (and dubious height), as reported by getSize() call in MarkerSvg.prototype.showWithField_

Reproduction steps

1. Go to https://google.github.io/blockly-samples/plugins/field-colour/test/index.html#renderer=zelos
2. Drag a colour picker block (the solid red oval) onto the workspace.
3. Open the JavaScript console and enter the following lines, one at a time:

   var marker = new Blockly.Marker();
   Blockly.getMainWorkspace().getMarkerManager().registerMarker('test', marker);
   marker.setCurNode(new Blockly.ASTNode(Blockly.ASTNode.types.FIELD, Blockly.getMainWorkspace().getAllBlocks()[0].getField('COLOUR')));
   

Observe that nothing happens. Compare to situation when renderer is set to geras or thrasos, when a blue oval is drawn around the colour field.

Stack trace

Screenshots

No response

[cpcallen]

@gonfunko: Would you add some screenshots of how things currently look for different full-block fields, and different possible renderings, so that accessibility partners can offer their views on what rendering is most preferable?