The WFS fallback does not respect `featureinfoLayer`

[MattiasSp]

The featureinfoLayer config parameter on WMS, WMTS or AGS_TILE layers is not taken into account.

Example:

• A WMS layer that is published as a group layer by the WMS Service contains a polygon layer, a linestring layer and a point layer as sublayers.
• The polygon layer is also defined in the config and referenced by the WMS group layer as its featureinfoLayer.
• When clicking on the group layer with the MultiSelect plugin disabled, the featureinfoLayer is queried and its results are displayed correctly.
• When activating the MultiSelect plugin and clicking again, it tries to query a WFS version of the group layer instead of the layer referenced by featureinfoLayer.

{
  "name": "registerenhet_yta",
  "source": "qgis_lm",
  "title": "Fastighetsytor",
  "group": "none",
  "visible": false,
  "queryable": true,
  "type": "WMS",
  "geometry": "geom",
  "attributes": [{ "name": "fastighet", "title": "Fastighetsbeteckning: " }]
  },
  {
  "name": "registerenheter_alla",
  "source": "qgis_lm",
  "title": "Fastighetsindelning",
  "group": "grupp1",
  "visible": true,
  "queryable": true,
  "featureinfoLayer": "registerenhet_yta",
  "style": "registerenheter_alla",
  "type": "WMS",
  "format": "image/png"
},

I am aware of the (undocumented) alternativeLayers parameter, which also solves problem described above, but I think the featureinfoLayer should be respected as well.

Perhaps any featureinfoLayer parameters on layers could be merged into the MultiSelect alternativeLayers config on initialization?