Rename taxonomy kinds from taxonomy to term, taxonomyTerm to taxonomy

And we have taken great measures to limit potential site breakage:

* For `disableKinds` and `outputs` we try to map from old to new values if possible, if not we print an ERROR that can be toggled off if not relevant.
* The layout lookup is mostly compatible with more options for the new `term` kind.

That leaves:

* Where queries in site.Pages using taxonomy/taxonomyTerm Kind values as filter.
* Other places where these kind value are used in the templates (classes etc.)

Fixes #6911
Fixes #7395

resources/page/page_kinds.go

@@ -20,18 +20,25 @@ const (
 
 	// The rest are node types; home page, sections etc.
 
-	KindHome         = "home"
-	KindSection      = "section"
-	KindTaxonomy     = "taxonomy"
-	KindTaxonomyTerm = "taxonomyTerm"
+	KindHome    = "home"
+	KindSection = "section"
+
+	// Note tha before Hugo 0.73 these were confusingly named
+	// taxonomy (now: term)
+	// taxonomyTerm (now: taxonomy)
+	KindTaxonomy = "taxonomy"
+	KindTerm     = "term"
 )
 
 var kindMap = map[string]string{
-	strings.ToLower(KindPage):         KindPage,
-	strings.ToLower(KindHome):         KindHome,
-	strings.ToLower(KindSection):      KindSection,
-	strings.ToLower(KindTaxonomy):     KindTaxonomy,
-	strings.ToLower(KindTaxonomyTerm): KindTaxonomyTerm,
+	strings.ToLower(KindPage):     KindPage,
+	strings.ToLower(KindHome):     KindHome,
+	strings.ToLower(KindSection):  KindSection,
+	strings.ToLower(KindTaxonomy): KindTaxonomy,
+	strings.ToLower(KindTerm):     KindTerm,
+
+	// Legacy, pre v0.53.0.
+	"taxonomyterm": KindTaxonomy,
 }
 
 // GetKind gets the page kind given a string, empty if not found.