Adds buildAttrMap(props) and setLayerAttr(obj, props, attrMap,
name, val) to utils.ts. The former replaces the PROP_BY_ATTR Map
construction (2 fewer lines per component), the latter replaces
the 6-line dynamic setter dispatch pattern used as the fallback
else block in 6 components.
For WMS, setLayerAttr returns false when no setter exists, so the
caller can fall back to setParams for non-method props.