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

2 files changed, 5 insertions, 4 deletions

diff --git a/tpl/strings/init_test.go b/tpl/strings/init_test.go
index b356896cf..dd15418c8 100644
--- a/tpl/strings/init_test.go
+++ b/tpl/strings/init_test.go
@@ -16,12 +16,13 @@ package strings
 import (
 	"testing"
 
+	"github.com/gohugoio/hugo/config"
+
 	"github.com/gohugoio/hugo/htesting/hqt"
 
 	qt "github.com/frankban/quicktest"
 	"github.com/gohugoio/hugo/deps"
 	"github.com/gohugoio/hugo/tpl/internal"
-	"github.com/spf13/viper"
 )
 
 func TestInit(t *testing.T) {
@@ -30,7 +31,7 @@ func TestInit(t *testing.T) {
 	var ns *internal.TemplateFuncsNamespace
 
 	for _, nsf := range internal.TemplateFuncsNamespaceRegistry {
-		ns = nsf(&deps.Deps{Cfg: viper.New()})
+		ns = nsf(&deps.Deps{Cfg: config.New()})
 		if ns.Name == name {
 			found = true
 			break
diff --git a/tpl/strings/strings_test.go b/tpl/strings/strings_test.go
index 6e14a408c..18c033793 100644
--- a/tpl/strings/strings_test.go
+++ b/tpl/strings/strings_test.go
@@ -17,14 +17,14 @@ import (
 	"html/template"
 	"testing"
 
+	"github.com/gohugoio/hugo/config"
 	"github.com/gohugoio/hugo/deps"
 
 	qt "github.com/frankban/quicktest"
 	"github.com/spf13/cast"
-	"github.com/spf13/viper"
 )
 
-var ns = New(&deps.Deps{Cfg: viper.New()})
+var ns = New(&deps.Deps{Cfg: config.New()})
 
 type tstNoStringer struct{}