Add additional test cases

Author: egregius313

go/ql/test/library-tests/semmle/go/dataflow/flowsources/local/file/test.go

@@ -1,6 +1,10 @@
 package test
 
-import "os"
+import (
+	"io/fs"
+	"io/ioutil"
+	"os"
+)
 
 func open() {
 	file, err := os.Open("file.txt") // $ source
@@ -27,3 +31,40 @@ func readFile() {
 	}
 	_ = data
 }
+
+func readFileIoUtil() {
+	data, err := ioutil.ReadFile("file.txt") // $source
+	if err != nil {
+		return
+	}
+	_ = data
+}
+
+func getFileFS() fs.ReadFileFS {
+	return nil
+}
+
+func readFileFs() {
+	data, err := fs.ReadFile(os.DirFS("."), "file.txt") // $source
+	if err != nil {
+		return
+	}
+	_ = data
+
+	dir := getFileFS()
+	data, err = dir.ReadFile("file.txt") // $source
+
+	if err != nil {
+		return
+	}
+	_ = data
+}
+
+func fsOpen() {
+	file, err := os.DirFS(".").Open("file.txt") // $source
+	if err != nil {
+		return
+	}
+	defer file.Close()
+	file.Read([]byte{1, 2, 3})
+}