all: Remove lib/util package (#9049)

Grab-bag packages are nasty, this cleans it up a little by splitting it
into topical packages sempahore, netutil, stringutil, structutil.

lib/model/folder.go

@@ -24,10 +24,11 @@ import (
 	"github.com/syncthing/syncthing/lib/osutil"
 	"github.com/syncthing/syncthing/lib/protocol"
 	"github.com/syncthing/syncthing/lib/scanner"
+	"github.com/syncthing/syncthing/lib/semaphore"
 	"github.com/syncthing/syncthing/lib/stats"
+	"github.com/syncthing/syncthing/lib/stringutil"
 	"github.com/syncthing/syncthing/lib/svcutil"
 	"github.com/syncthing/syncthing/lib/sync"
-	"github.com/syncthing/syncthing/lib/util"
 	"github.com/syncthing/syncthing/lib/versioner"
 	"github.com/syncthing/syncthing/lib/watchaggregator"
 )
@@ -39,7 +40,7 @@ type folder struct {
 	stateTracker
 	config.FolderConfiguration
 	*stats.FolderStatisticsReference
-	ioLimiter *util.Semaphore
+	ioLimiter *semaphore.Semaphore
 
 	localFlags uint32
 
@@ -95,7 +96,7 @@ type puller interface {
 	pull() (bool, error) // true when successful and should not be retried
 }
 
-func newFolder(model *model, fset *db.FileSet, ignores *ignore.Matcher, cfg config.FolderConfiguration, evLogger events.Logger, ioLimiter *util.Semaphore, ver versioner.Versioner) folder {
+func newFolder(model *model, fset *db.FileSet, ignores *ignore.Matcher, cfg config.FolderConfiguration, evLogger events.Logger, ioLimiter *semaphore.Semaphore, ver versioner.Versioner) folder {
 	f := folder{
 		stateTracker:              newStateTracker(cfg.ID, evLogger),
 		FolderConfiguration:       cfg,
@@ -426,7 +427,7 @@ func (f *folder) pull() (success bool, err error) {
 
 	// Pulling failed, try again later.
 	delay := f.pullPause + time.Since(startTime)
-	l.Infof("Folder %v isn't making sync progress - retrying in %v.", f.Description(), util.NiceDurationString(delay))
+	l.Infof("Folder %v isn't making sync progress - retrying in %v.", f.Description(), stringutil.NiceDurationString(delay))
 	f.pullFailTimer.Reset(delay)
 
 	return false, err