patch 8.2.2343: Vim9: return type of readfile() is any

Problem:    Vim9: return type of readfile() is any.
Solution:   Add readblob() so that readfile() can be expected to always
            return a list of strings. (closes #7671)
diff --git a/src/filepath.c b/src/filepath.c
index 0db0dcf..81fe749 100644
--- a/src/filepath.c
+++ b/src/filepath.c
@@ -1640,11 +1640,11 @@
 /*
  * "readfile()" function
  */
-    void
-f_readfile(typval_T *argvars, typval_T *rettv)
+    static void
+read_file_or_blob(typval_T *argvars, typval_T *rettv, int always_blob)
 {
     int		binary = FALSE;
-    int		blob = FALSE;
+    int		blob = always_blob;
     int		failed = FALSE;
     char_u	*fname;
     FILE	*fd;
@@ -1796,7 +1796,8 @@
 
 			if (dest < buf)
 			{
-			    adjust_prevlen = (int)(buf - dest); // must be 1 or 2
+			    // must be 1 or 2
+			    adjust_prevlen = (int)(buf - dest);
 			    dest = buf;
 			}
 			if (readlen > p - buf + 1)
@@ -1867,6 +1868,24 @@
 }
 
 /*
+ * "readblob()" function
+ */
+    void
+f_readblob(typval_T *argvars, typval_T *rettv)
+{
+    read_file_or_blob(argvars, rettv, TRUE);
+}
+
+/*
+ * "readfile()" function
+ */
+    void
+f_readfile(typval_T *argvars, typval_T *rettv)
+{
+    read_file_or_blob(argvars, rettv, FALSE);
+}
+
+/*
  * "resolve()" function
  */
     void