chore: make FastAbs comment more easy to understand (#6692)

filepath.go

@@ -24,6 +24,8 @@ import (
 // FastAbs is an optimized version of filepath.Abs for Unix systems,
 // since we don't expect the working directory to ever change once
 // Caddy is running. Avoid the os.Getwd() syscall overhead.
+// It's overall the same as stdlib's implementation, the difference
+// being cached working directory.
 func FastAbs(path string) (string, error) {
 	if filepath.IsAbs(path) {
 		return filepath.Clean(path), nil

filepath_windows.go

@@ -18,8 +18,10 @@ import (
 	"path/filepath"
 )
 
-// FastAbs can't be optimized on Windows because the
-// syscall.FullPath function takes an input.
+// FastAbs can't be optimized on Windows because there
+// are special file paths that require the use of syscall.FullPath
+// to handle correctly.
+// Just call stdlib's implementation which uses that function.
 func FastAbs(path string) (string, error) {
 	return filepath.Abs(path)
 }