[internal/filter] Add bridge from filterlog to filterottl (open-telem…

…etry#22789)

This PR adds a bridge between `filterlog.NewSkipExpr` and
`filterottl.NewBoolExprForLog` behind a feature gate. With the feature
gate enabled, any component using `filterlog.NewSkipExpr` will start
using OTTL behind the scenes.

Related to
open-telemetry#18643
Related to
open-telemetry#18642

Added tests comparing the output of the existing config and the bridge.

internal/filter/filterlog/filterlog.go

@@ -7,17 +7,31 @@ import (
 	"context"
 	"fmt"
 
+	"go.opentelemetry.io/collector/featuregate"
+
 	"github.com/open-telemetry/opentelemetry-collector-contrib/internal/filter/expr"
 	"github.com/open-telemetry/opentelemetry-collector-contrib/internal/filter/filterconfig"
 	"github.com/open-telemetry/opentelemetry-collector-contrib/internal/filter/filtermatcher"
+	"github.com/open-telemetry/opentelemetry-collector-contrib/internal/filter/filterottl"
 	"github.com/open-telemetry/opentelemetry-collector-contrib/internal/filter/filterset"
 	"github.com/open-telemetry/opentelemetry-collector-contrib/pkg/ottl/contexts/ottllog"
 )
 
+var useOTTLBridge = featuregate.GlobalRegistry().MustRegister(
+	"filter.filterlog.useOTTLBridge",
+	featuregate.StageAlpha,
+	featuregate.WithRegisterDescription("When enabled, filterlog will convert filterlog configuration to OTTL and use filterottl evaluation"),
+	featuregate.WithRegisterReferenceURL("https://github.com/open-telemetry/opentelemetry-collector-contrib/issues/18642"),
+)
+
 // NewSkipExpr creates a BoolExpr that on evaluation returns true if a log should NOT be processed or kept.
 // The logic determining if a log should be processed is based on include and exclude settings.
 // Include properties are checked before exclude settings are checked.
 func NewSkipExpr(mp *filterconfig.MatchConfig) (expr.BoolExpr[ottllog.TransformContext], error) {
+
+	if useOTTLBridge.IsEnabled() {
+		return filterottl.NewLogSkipExprBridge(mp)
+	}
 	var matchers []expr.BoolExpr[ottllog.TransformContext]
 	inclExpr, err := newExpr(mp.Include)
 	if err != nil {