Misc config loading fixes

The main motivation behind this is simplicity and correctnes, but the new small config library is also faster:

```
BenchmarkDefaultConfigProvider/Viper-16         	  252418	      4546 ns/op	    2720 B/op	      30 allocs/op
BenchmarkDefaultConfigProvider/Custom-16        	  450756	      2651 ns/op	    1008 B/op	       6 allocs/op
```

Fixes #8633
Fixes #8618
Fixes #8630
Updates #8591
Closes #6680
Closes #5192

1 files changed, 5 insertions, 4 deletions

diff --git a/tpl/transform/unmarshal_test.go b/tpl/transform/unmarshal_test.go
index ec81c316a..85e3610d1 100644
--- a/tpl/transform/unmarshal_test.go
+++ b/tpl/transform/unmarshal_test.go
@@ -19,13 +19,14 @@ import (
 	"strings"
 	"testing"
 
+	"github.com/gohugoio/hugo/config"
+
 	"github.com/gohugoio/hugo/common/hugio"
 	"github.com/gohugoio/hugo/resources/resource"
 
 	"github.com/gohugoio/hugo/media"
 
 	qt "github.com/frankban/quicktest"
-	"github.com/spf13/viper"
 )
 
 const (
@@ -79,7 +80,7 @@ func (t testContentResource) Key() string {
 }
 
 func TestUnmarshal(t *testing.T) {
-	v := viper.New()
+	v := config.New()
 	ns := New(newDeps(v))
 	c := qt.New(t)
 
@@ -173,7 +174,7 @@ a;b;c`, mime: media.CSVType}, map[string]interface{}{"DElimiter": ";", "Comment"
 }
 
 func BenchmarkUnmarshalString(b *testing.B) {
-	v := viper.New()
+	v := config.New()
 	ns := New(newDeps(v))
 
 	const numJsons = 100
@@ -196,7 +197,7 @@ func BenchmarkUnmarshalString(b *testing.B) {
 }
 
 func BenchmarkUnmarshalResource(b *testing.B) {
-	v := viper.New()
+	v := config.New()
 	ns := New(newDeps(v))
 
 	const numJsons = 100