minifiers: Update deprecation handling

1. With minify.tdewolff.css and minify.tdewolff.svg, check
   for "decimals" instead of "decimal"

2. Add deprecation messages for:

  - minify.tdewolff.css.decimals
  - minify.tdewolff.svg.decimals
  - minify.tdewolff.html.keepconditionalcomments
  - config root minify (bool)
  - config root minifyoutput (bool)

3. Deprecate minify.tdewolff.css.keepcss2 in favor
   of minify.tdewolff.css.version

4. Refactor minify configuration tests

Closes #11893
Closes #13947
Closes #13948

minifiers/minifiers_test.go

@@ -26,7 +26,6 @@ import (
 	"github.com/gohugoio/hugo/minifiers"
 	"github.com/gohugoio/hugo/output"
 	"github.com/spf13/afero"
-	"github.com/tdewolff/minify/v2/html"
 )
 
 func TestNew(t *testing.T) {
@@ -166,51 +165,3 @@ func TestBugs(t *testing.T) {
 		c.Assert(b.String(), qt.Equals, test.expectedMinString)
 	}
 }
-
-// Renamed to Precision in v2.7.0. Check that we support both.
-func TestDecodeConfigDecimalIsNowPrecision(t *testing.T) {
-	c := qt.New(t)
-	v := config.New()
-	v.Set("minify", map[string]any{
-		"disablexml": true,
-		"tdewolff": map[string]any{
-			"css": map[string]any{
-				"decimal": 3,
-			},
-			"svg": map[string]any{
-				"decimal": 3,
-			},
-		},
-	})
-
-	conf := testconfig.GetTestConfigs(nil, v).Base.Minify
-
-	c.Assert(conf.Tdewolff.CSS.Precision, qt.Equals, 3)
-}
-
-// Issue 9456
-func TestDecodeConfigKeepWhitespace(t *testing.T) {
-	c := qt.New(t)
-	v := config.New()
-	v.Set("minify", map[string]any{
-		"tdewolff": map[string]any{
-			"html": map[string]any{
-				"keepEndTags": false,
-			},
-		},
-	})
-
-	conf := testconfig.GetTestConfigs(nil, v).Base.Minify
-
-	c.Assert(conf.Tdewolff.HTML, qt.DeepEquals,
-		html.Minifier{
-			KeepComments:        false,
-			KeepSpecialComments: true,
-			KeepDefaultAttrVals: true,
-			KeepDocumentTags:    true,
-			KeepEndTags:         false,
-			KeepQuotes:          false,
-			KeepWhitespace:      false,
-		},
-	)
-}